SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549


                                  SCHEDULE 13D

                    Under the Securities Exchange Act of 1934

                                BSB BANCORP, INC.
                             -----------------------
                                (Name of Issuer)

                     Common Stock, par value $.01 per share
                -------------------------------------------------
                         (Title of Class of Securities)

                                   055652-10-1
                 -----------------------------------------------
                      (CUSIP Number of Class of Securities)

                              Mr. Daryl R. Forsythe
                      President and Chief Executive Officer
                                NBT Bancorp Inc.
                              52 South Broad Street
                             Norwich, New York 13815
                                 (607) 337-2265
    ------------------------------------------------------------------------
            (Name, Address and Telephone Number of Person Authorized
                     to Receive Notices and Communications)

                                    Copy to:

                              Brian D. Alprin, Esq.
                             Laurence S. Lese, Esq.
                          Duane, Morris & Heckscher LLP
                         1667 K Street, N.W., Suite 700
                             Washington, D.C. 20006
                                 (202) 776-7800

                                       1





                                 April 19, 2000
                     ---------------------------------------
                          (Date of Event which Requires
                            Filing of this Statement)

If the filing person has previously  filed a statement on Schedule 13G to report
the  acquisition  which  is the  subject  of  this  Statement  because  of  Rule
13d-1(b)(3) or (4), check the following:

                                       [ ]

Check the following box if a fee is being paid with this Statement:

                                      [ ]

- --------------------------------------------------------------------------------
(1)      NAMES OF REPORTING PERSONS
         S.S. OR I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS

         NBT BANCORP INC.
         16-1268674
- --------------------------------------------------------------------------------
(2)      CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP:
                             (a)      [ ]
                             (b)      [ ]
- --------------------------------------------------------------------------------
(3)      SEC USE ONLY

- --------------------------------------------------------------------------------
(4)      SOURCE OF FUNDS*

         WC/00
- --------------------------------------------------------------------------------
(5)      CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED
         PURSUANT TO ITEMS 2(d) or 2(e)
                                      [ ]
- --------------------------------------------------------------------------------
(6)      CITIZENSHIP OR PLACE OF ORGANIZATION

         DELAWARE
- --------------------------------------------------------------------------------
NUMBER OF SHARES                             (7)     SOLE VOTING POWER
BENEFICIALLY OWNED BY                                   2,041,052(1)
EACH REPORTING PERSON                                ---------------------
WITH:                                        (8)     SHARED VOTING

                                                             -0-
                                                     ---------------------


                                        2






                                            (9)     SOLE DISPOSITIVE
                                                       2,041,052(1)
                                                    -------------------------
                                            (10)    SHARED DISPOSITIVE
                                                           -0-

- -------------------------------------------------------------------------------
(11)     AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING
         PERSON

         2,041,052(1)

- -------------------------------------------------------------------------------
(12)     CHECK BOX IF THE AGGREGATE AMOUNT IN ROW 11 EXCLUDES CERTAIN
SHARES*                                               [ ]

         N/A

- -------------------------------------------------------------------------------
(13)     PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 11

         APPROXIMATELY 16.6%(2)
- -------------------------------------------------------------------------------
(14)     TYPE OF REPORTING PERSON*

         CO
- -------------------------------------------------------------------------------

*        SEE INSTRUCTIONS BEFORE FILLING OUT!

(1)      The  shares  of  Issuer   common  stock  covered  by  this  report  are
         purchasable  by Reporting  Person upon exercise of an option granted by
         Issuer to Reporting  Person as of April 19, 2000, and described in Item
         4 of this report. Prior to the exercise of the option, Reporting Person
         is not  entitled  to any  rights as a  stockholder  of Issuer as to the
         shares covered by the option. The option may be exercised only upon the
         happening  of certain  events  referred to in Item 4, none of which has
         occurred as of the date hereof.  Reporting Person  expressly  disclaims
         beneficial  ownership  of any of the  shares of common  stock of Issuer
         which are  purchasable by Reporting  Person upon exercise of the option
         until such time as Reporting  Person purchases any such shares upon any
         such exercise.  The number of shares indicated  represents 19.9% of the
         10,256,545  total  outstanding  shares of common  stock of Issuer as of
         March 31, 2000,  excluding shares issuable upon exercise of the option.
         See Item 4 below for a discussion of the Option.

(2)      After giving effect to the exercise of the option as described herein.

                                        3





ITEM 1.    SECURITY AND ISSUER.

This statement on Schedule 13D (the "Schedule 13D") relates to the common stock,
$.01 par value per share (the  "Shares" or the "Issuer  Common  Stock"),  of BSB
Bancorp, Inc., a Delaware corporation ("Issuer"). The principal executive office
of Issuer is located at 58-68 Exchange Street, Binghamton, New York 13901.

The  information   set  forth  in  the  Exhibits  hereto  is  hereby   expressly
incorporated herein by reference and the responses to each item of this Schedule
13D are qualified in their entirety by the provisions of such Exhibits.

ITEM 2.    IDENTITY AND BACKGROUND.

(a)-(c) This Schedule 13D is filed by NBT Bancorp  Inc., a Delaware  corporation
("Reporting Person").

The business address of Reporting Person is 52 South Broad Street,  Norwich, New
York  13815.  The  principal  business  of  Reporting  Person is a bank  holding
company.

To the best of Reporting  Person's  knowledge  as of the date hereof,  the name;
business address;  present principal  occupation or employment;  name, principal
business  and address of any  corporation  or other  organization  in which such
employment is conducted;  and citizenship of each executive officer and director
of Reporting Person is set forth in Schedule I hereto. The information contained
in Schedule I is incorporated herein by reference.

(d)-(e) During the last five years,  neither  Reporting  Person nor, to the best
knowledge of Reporting  Person,  any of the  executive  officers or directors of
Reporting Person, has been convicted in a criminal proceeding (excluding traffic
violations or similar misdemeanors),  or been a party to a civil proceeding of a
judicial or  administrative  body of competent  jurisdiction  and as a result of
such proceeding was or is subject to a judgment, decree or final order enjoining
future violations of, or prohibiting or mandating activities subject to, federal
or state securities laws or finding any violation with respect to such items.

ITEM 3.    SOURCE AND AMOUNT OF FUNDS OR OTHER CONSIDERATION.

The Option  (defined in Item 4 below) to acquire Shares was granted by Issuer to
Reporting  Person  as an  inducement  to  Reporting  Person's  entering  into an
Agreement  and Plan of  Merger,  dated  as of April  19,  2000,  by and  between
Reporting Person and Issuer (the "Plan of Merger"),  providing for the merger of
Issuer  into  Reporting   Person  with  Reporting  Person  being  the  surviving
corporation  (the "Merger").  Pursuant to the Plan of Merger,  each  outstanding
Share will be  converted  into the right to receive two shares of common  stock,
par value $.01 per share, of Reporting Person ("Reporting Person Common Stock").
The  Merger is  subject to the  approval  of  Issuer's  and  Reporting  Person's
stockholders, respectively, regulatory approvals, and the satisfaction or waiver
of various other conditions, as more fully

                                        4




described in the Plan of Merger.  None of the Purchase Events (defined in Item 4
below) permitting the exercise of the Option has occurred as of the date hereof.
In the event that the Option becomes  exercisable and Reporting Person wishes to
purchase the Shares subject thereto,  Reporting Person anticipates that it would
fund the exercise price with working capital or through other financing  sources
available  to  Reporting  Person at the time of  exercise.  Had the Option  been
exercisable  on March 31,  2000,  when Issuer had a total of  10,256,545  Shares
issued and  outstanding,  the total exercise  price would have been  $37,759,462
(assuming full exercise of the Option). A copy of the Plan of Merger is attached
hereto as Exhibit 2.1. See Item 4 below.

ITEM 4.    PURPOSE OF THE TRANSACTION.

The information set forth in Item 3 is hereby incorporated herein by reference.

The purpose of the  transaction  is for Issuer to merge with and into  Reporting
Person, with Reporting Person being the surviving entity. In connection with the
Plan of Merger and in consideration thereof, Issuer and Reporting Person entered
into that certain Stock Option Agreement (the "Option  Agreement"),  dated April
19, 2000,  whereby Issuer granted to Reporting  Person an option (the "Option").
Under the Option,  Reporting  Person may purchase,  under certain  circumstances
described  therein,  up to 19.9% of the total  number of  outstanding  shares of
Issuer  Common Stock as of the first date that the Option  becomes  exercisable.
The cash purchase  price per Share of the Option is equal to $18.50,  subject to
antidilution adjustment as provided therein (the "Purchase Price"). On March 31,
2000,  Issuer had a total of 10,256,545 Shares of Issuer Common Stock issued and
outstanding;  had the Option been exercisable on that date, a total of 2,041,052
Shares would have been issuable under the Option. The Option,  being exercisable
for approximately 19.9% of the outstanding Shares, would represent approximately
16.6% of the  Shares  that  would be  outstanding  after  giving  effect  to the
exercise of the Option.

On April 19, 2000,  Reporting  Person  executed a second option  agreement  with
Issuer.  In that  agreement,  Reporting  Person is the  issuer and Issuer is the
grantee.  That  agreement's  provisions are  substantially  the same (except for
option price per share) as those in the Option  Agreement except the position of
each party to the agreement has been reversed.

Reporting Person may exercise the Option, in whole or part, at any time and from
time to time following the  occurrence of a Purchase  Event (as defined  below);
provided, however, that the Option will terminate and be of no further force and
effect  upon  the  earliest  to  occur  of  the  following   events  (which  are
collectively referred to as an "Exercise Termination Event"):

         (i)   The time immediately prior to the effective time of the Merger;

         (ii)  12 months after the first occurrence of a Purchase Event;

         (iii) 12 months after the  termination of the Plan of Merger  following
               the occurrence of a

                                        5






               Preliminary Purchase Event (as defined below);

         (iv)  upon the termination of the Plan of Merger,  if no Purchase Event
               or  Preliminary   Purchase  Event  has  occurred  prior  to  such
               termination, by Issuer pursuant to Section 7.01(d) of the Plan of
               Merger,  both parties  pursuant to Section 7.01(a) of the Plan of
               Merger,  or by either  party  pursuant to Section  7.01(b) of the
               Plan of Merger;

         (v)   upon termination of the Plan of Merger,  by either party pursuant
               to Sections 7.01(e) or (f) of the Plan of Merger based on (A) the
               required  votes of  Reporting  Person's  stockholders  not  being
               obtained  for any reason at the  Reporting  Person  Stockholders'
               Meeting  (as  defined in the Plan of Merger) or (B) the  required
               vote of Issuer's  stockholders  not being  received at the Issuer
               Stockholders'  Meeting (as defined in the Plan of Merger),  if no
               Purchase Event or Preliminary  Purchase Event shall have occurred
               prior to the meeting of Issuer's stockholders (or any adjournment
               or postponement thereof) held to vote on the Plan of Merger; or

         (vi)  12  months  after  the  termination  of the  Plan of  Merger,  by
               Reporting  Person pursuant to Section 7.01(c) thereof as a result
               of a breach by Issuer,  or by Reporting Person or Issuer pursuant
               to Section 7.01(g) or (h) of the Plan of Merger.

The term  "Preliminary  Purchase  Event"  means any of the  following  events or
transactions  occurring  on or after the date  hereof  and prior to an  Exercise
Termination Event:

         (i)   Issuer without having received  Reporting  Person's prior written
               consent,  shall  have  entered  into  any  letter  of  intent  or
               definitive agreement to engage in an Acquisition  Transaction (as
               defined  below)  with any person (as  defined  below)  other than
               Reporting  Person or any of its  subsidiaries  (each a "Reporting
               Person  Subsidiary")  or the Board of  Directors  of Issuer shall
               have  recommended  that the  stockholders  of Issuer  approve  or
               accept any Acquisition  Transaction  with any Person (as the term
               "person"  is defined in  Sections  3(a)(9)  and  13(d)(3)  of the
               Exchange Act and the rules and regulations thereunder) other than
               Reporting Person or any Reporting Person Subsidiary.

         (ii)  Any Person (other than  Reporting  Person,  any Reporting  Person
               Subsidiary  or  any  current  affiliate  of  Issuer)  shall  have
               acquired  beneficial  ownership of 20% or more of the outstanding
               shares of Issuer Common Stock;

         (iii) (a) Any Person  (other  than  Reporting  Person or any  Reporting
               Person Subsidiary) shall have made a bona fide proposal to Issuer
               or, by a public announcement or written  communication that is or
               becomes   the   subject  of  public   disclosure,   to   Issuer's
               stockholders prior to the Issuer Stockholders'  Meeting to engage
               in an Acquisition Transaction (including, without limitation, any
               situation in which any Person other than Reporting  Person or any
               Reporting Person Subsidiary shall have commenced (as such

                                        6





               term is defined in Rule 14d-2  promulgated under the Exchange Act
               or shall have filed a registration statement under the Securities
               Act of 1933, as amended (the "Securities Act"), with respect to a
               tender  offer or exchange  offer to purchase any shares of Issuer
               Common Stock such that,  upon  consummation  of such offer,  such
               person would have Beneficial Ownership of 20% or more of the then
               outstanding shares of Issuer Common Stock and

               (b) The  stockholders  of Issuer do not approve the Merger at the
               Issuer Stockholders' Meeting;

         (iv)  There shall exist a willful or intentional  breach under the Plan
               of Merger by  Issuer  and such  breach  would  entitle  Reporting
               Person to terminate the Plan of Merger; or

         (v)   The Issuer  Stockholders'  Meeting to be held for the  purpose of
               voting on the Plan of Merger shall not have been held pursuant to
               the  Plan  of  Merger  or  shall  have  been  canceled  prior  to
               termination of the Plan of Merger,  or for any reason  whatsoever
               Issuer's  Board of Directors  shall have failed to recommend,  or
               shall have withdrawn or modified in a manner adverse to Reporting
               Person the  recommendation  of Issuer's  Board of Directors  that
               Issuer's stockholders approve the Plan of Merger, or if Issuer or
               Issuer's  Board of Directors  fails to oppose any proposal of the
               type  described at P.  (iii)(a)  above by any Person  (other than
               Reporting Person or any Reporting Person Subsidiary).

Under  the  Option  Agreement,  "Acquisition  Transaction"  means  (x) a merger,
consolidation or other business  combination  involving Issuer,  (y) a purchase,
lease or other  acquisition of all or substantially all of the assets of Issuer,
(z) a purchase or other acquisition (including by way of merger,  consolidation,
share  exchange or otherwise) of beneficial  ownership (as the term  "beneficial
ownership" is defined in Regulation  13d-3(a) of the Exchange Act) of securities
representing 20% or more of the voting power of Issuer; provided,  however, that
"Acquisition  Transaction" will not include a transaction entered into after the
termination  of the Plan of Merger in which the Issuer is the surviving  entity,
if in connection with such transaction,  no person acquires Beneficial Ownership
of 20% or more of the total voting power of the Issuer to be  outstanding  after
giving effect to such  transaction  and in which the  aggregate  voting power of
Issuer  acquired  by all persons is less than 33% of the total  voting  power of
Issuer.

The term  "Purchase  Event" means any of the  following  events or  transactions
occurring  on or after the date of the Plan of Merger  and prior to an  Exercise
Termination Event:

         (i)   The acquisition by any Person (other than Reporting Person or any
               Reporting Person Subsidiary) of beneficial  ownership (other than
               on behalf of the  Issuer) of 20% or more of the then  outstanding
               Issuer Common Stock;

         (ii)  The occurrence of a Preliminary  Purchase  Event  described in P.
               (i) of that definition; or

                                        7





         (iii) The  termination  of the  Plan  of  Merger  by  Reporting  Person
               pursuant to Section  7.01(c)  thereof as a result of a willful or
               intentional  breach by Issuer  or by  Reporting  Person or Issuer
               pursuant to Section 7.01(g) or (h) of the Plan of Merger.

The Option  Agreement  grants  certain  registration  rights (the  "Registration
Rights") to  Reporting  Person  with  respect to the Shares  represented  by the
Option.  The  terms of such  Registration  Rights  are set  forth in the  Option
Agreement.

A copy of the Option  Agreement  is attached  hereto as Exhibit  2.5. The option
agreement of Reporting Person as issuer is attached hereto as Exhibit 2.6.

The purpose of the Option Agreement is to facilitate consummation of the Merger.

(a)-(j) Upon  consummation  of the Merger as contemplated by the Plan of Merger,
(a) Issuer will be merged into  Reporting  Person and the separate  existence of
Issuer will  terminate,  (b)  Reporting  Person by operation of law will own the
assets and be subject to the  liabilities  of Issuer in exchange  for  Reporting
Person Common Stock to be distributed to holders of the Issuer's securities, (c)
the Board of Directors of Issuer will be terminated and some of its members will
become  members  of  the  Board  of  Directors  of  Reporting  Person,  (d)  the
Certificate of Incorporation and Bylaws of Issuer will be canceled,  (e) all the
Shares will be  canceled  upon  effectiveness  of the Merger and the Shares will
cease to be  authorized  to be  traded in Nasdaq  National  Market,  and (f) the
Shares will become eligible for termination of registration  pursuant to Section
12(g)(4) of the Securities Exchange Act of 1934, as amended.

ITEM 5.    INTEREST IN SECURITIES OF THE ISSUER.

(a)-(b)  The number of Shares  covered by the Option is equal to 19.9% of Issuer
Common Stock based on the Shares issued and  outstanding  on the date the Option
becomes  exercisable or 16.6% of the shares of Issuer Common Stock that would be
outstanding  after giving  effect to the exercise of the Option.  Had the Option
been  exercisable on March 31, 2000, a total of 2,041,052 Shares would have been
issuable under the Option.

Prior to the exercise of the Option, Reporting Person (i) is not entitled to any
rights as a  stockholder  of Issuer as to the  Shares  covered by the option and
(ii)  disclaims  any  beneficial  ownership of the shares of Issuer Common Stock
which are  purchasable  by Reporting  Person upon exercise of the Option because
the Option is exercisable only in the limited circumstances  referred to in Item
4 above,  none of which has occurred as of the date  hereof.  If the Option were
exercised,  Reporting  Person would have the sole right to vote or to dispose of
the shares of Issuer Common Stock issued as a result of such exercise.

(c) Other  than as set forth in this Item 5, to the best of  Reporting  Person's
knowledge as of the date hereof (i) neither  Reporting Person nor any subsidiary
or  affiliate  of  Reporting  Person  nor any of  Reporting  Person's  executive
officers or directors  beneficially  owns any shares of Issuer Common Stock, and
(ii)

                                        8





there have been no  transactions  in the shares of Issuer Common Stock  effected
during  the  past 60 days by  Reporting  Person,  nor to the  best of  Reporting
Person's knowledge, by any subsidiary or affiliate of Reporting Person or any of
Reporting Person's executive officers or directors.

(d) No other person is known by Reporting Person to have the right to receive or
the power to direct the receipt of dividends from, or the proceeds from the sale
of, the Issuer Common Stock  obtainable by Reporting Person upon exercise of the
Option.

(e) Not applicable.

ITEM 6.    CONTRACTS, ARRANGEMENTS, UNDERSTANDINGS OR RELATIONSHIPS WITH RESPECT
TO SECURITIES OF THE ISSUER.

The disclosure set forth in Items 3 and 4 above regarding the Plan of Merger and
Option Agreement is hereby incorporated herein by reference.

As a part of the  Plan of  Merger,  each of  Issuer's  directors  and  executive
officers  has  agreed to vote or cause to be voted  all of his or her  Shares in
favor  of the  Plan  of  Merger  and the  Merger;  in his or her  capacity  as a
stockholder of Issuer not to encourage or solicit,  initiate or hold discussions
or  negotiations  with,  or provide any  information  to, any person  other than
Reporting  Person or an affiliate of Reporting  Person,  concerning  any merger,
sale  of all or  substantially  all of its  assets  and  liabilities  not in the
ordinary  course  of  business,  sale of  shares  of  capital  stock or  similar
transaction involving Issuer or otherwise  inconsistent with the Plan of Merger;
and to use his or her best efforts to take or cause to be taken all action,  and
to do or  cause  to be  done  all  things  necessary,  proper  or  advisable  to
consummate and make effective the Merger contemplated by the Plan of Merger.

ITEM 7.    MATERIAL TO BE FILED AS EXHIBITS.

EXHIBIT    DESCRIPTION

2.1        Agreement  and Plan of  Merger,  dated as of April 19,  2000,  by and
           between NBT Bancorp Inc. and BSB Bancorp, Inc.*

2.2        Form of Plan of Merger between BSB Bank & Trust Company and NBT Bank,
           National  Association,  is part of the  Agreement and Plan of Merger,
           which is filed as Exhibit 2.1 above.*

2.3        The BSB Stockholder Agreement, dated as of April 19, 2000, is part of
           the  Agreement  and Plan of  Merger,  which is filed as  Exhibit  2.1
           above.*

2.4        The NBT Stockholder Agreement, dated as of April 19, 2000, is part of
           the Agreement

                                        9






           and Plan of Merger, which is filed as Exhibit 2.1 above.*

2.5        BSB Stock Option Agreement,  dated April 19, 2000, by and between BSB
           Bancorp,  Inc. as "Issuer"  and NBT Bancorp Inc. as "Grantee" is part
           of the  Agreement  and Plan of Merger,  which is filed as Exhibit 2.1
           above.*

2.6        NBT Stock Option Agreement,  dated April 19, 2000, by and between NBT
           Bancorp Inc. as "Issuer"  and BSB Bancorp,  Inc. as "Grantee" is part
           of the  Agreement  and Plan of Merger,  which is filed as Exhibit 2.1
           above.*

*  Incorporated  by  reference  to  the  corresponding  exhibit  number  in  the
Registrant's Current Report on SEC Form 8-K filed by the Registrant on April 28,
2000, SEC File No. 0-14703.

                                       10






                                    SIGNATURE

After  reasonable  inquiry and to the best of my knowledge and belief, I certify
that this statement is true, complete and correct.

                                             NBT BANCORP INC.

                                             By:     /s/ Daryl R. Forsythe
                                                     ---------------------------
                                             Name:   Daryl R. Forsythe
                                             Title:  President and Chief
                                                     Executive Officer

Dated:  April 27, 2000




                                       11




                                   SCHEDULE I


              DIRECTORS AND EXECUTIVE OFFICERS OF NBT BANCORP INC.

           The following table sets forth the name, business address and present
principal  occupation or  employment  of each director and executive  officer of
Reporting Person.  Each such person is a U.S. citizen,  and the business address
of each such person is 52 South Broad Street, Norwich, New York 13815.

Name and Business                        Present Principal
    Address                                 Occupation
    -------                                 ----------

*Daryl R. Forsythe                     President and Chief Executive Officer

*Everett A. Gilmour                    Chairman, Retired

Joe C. Minor                           President and Chief Operating Officer,
                                       NBT Financial Services, Inc.

Michael J. Chewens                     Executive Vice President, Chief Financial
                                       Officer

John D. Roberts                        Senior Vice President and Secretary

*J. Peter Chaplin                      Retired

*Peter B. Gregory                      Partner, Gatehouse Antiques

*William C. Gumble                     Retired

*Bruce D. Howe                         President of John T. Howe, Inc.
                                       (fuel and heating oil company)

*Andrew S. Kowalczyk, Jr.              Partner, Kowalczyk, Tolles, Deery
                                       & Johnston, attorneys

*Dan B. Marshman                       Marshman Farms, Inc.

*John G. Martines                      Chief Executive Officer, LA Bank, N.A.

                                       12





*John C. Mitchell                      President, I.L. Richer Co.
                                       (agribusiness)

*William L. Owens                      Partner, Stafford, Trombley, Owens
                                       & Curtin, P.C., attorneys

*Paul O. Stillman                      Chairman, Preferred Mutual
                                       Insurance Co.

*Director of NBT Bancorp Inc.

                                       13