<PAGE>   1
                UNITED STATES SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                                  FORM 10-K/A-1

(Mark One)
[ X ] ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES
         EXCHANGE ACT OF 1934
For the fiscal year ended December 31, 1999

                                       OR

[ ] TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE
ACT OF 1934 For the transition period from __________ to __________

                        Commission File Number: 001-13094

                               DIME BANCORP, INC.
             (Exact name of registrant as specified in its charter)

<TABLE>

<S>                                                                   <C>
                          DELAWARE                                                11-3197414
(State or other jurisdiction of incorporation or organization)        (I.R.S. Employer Identification No.)

           589 FIFTH AVENUE, NEW YORK, NEW YORK                                     10017
         (Address of principal executive offices)                                 (Zip code)
</TABLE>

                                 (212) 326-6170
               Registrant's telephone number, including area code

           Securities registered pursuant to Section 12(b) of the Act:

<TABLE>
<S>                                  <C>
     Title of each class              Name of each exchange on which registered
Common Stock, $0.01 par value                 New York Stock Exchange
    Stock Purchase Rights                      New York Stock Exchange
</TABLE>

Securities registered pursuant to Section 12(g) of the Act:  None

        Indicate by check mark whether the registrant (1) has filed all reports
required to be filed by Section 13 or 15(d) of the Securities Exchange Act of
1934 during the preceding 12 months (or for such shorter period that the
registrant was required to file such reports), and (2) has been subject to such
filing requirements for the past 90 days. Yes X No____

        Indicate by check mark if disclosure of delinquent filers pursuant to
Item 405 of Regulation S-K is not contained herein, and will not be contained,
to the best of registrant's knowledge, in definitive proxy or information
statements incorporated by reference in Part III of this Form 10-K or any
amendment to this Form 10-K. [ ]

        The aggregate market value of the shares of registrant's common stock
held by non-affiliates (assuming, solely for purposes of this Form, that all
directors are affiliates) was $1,322,517,641 as of February 29, 2000 (based on
the closing New York Stock Exchange price on such date).

        The number of shares of common stock of the registrant outstanding as of
February 29, 2000 was 111,240,660 shares.
<PAGE>   2
The amendment on Form 10-K/A-1 is being filed to (i) revise the date of the
Report of Independent Auditors in Item 8, "Financial Statements and
Supplementary Data" as set forth on page F-1 of the Annual Report on Form 10-K
filed with the Commission on March 30, 2000 (the "1999 Form 10-K") and (ii)
delete the word "Unaudited" from the heading of Note 28 of Notes to Consolidated
Financial Statements in Item 8, "Financial Statements and Supplementary Data" as
set forth on page F-51 of the 1999 Form 10-K.


ITEM 8.  Financial Statements and Supplementary Data

                         REPORT OF INDEPENDENT AUDITORS

The Board of Directors and Shareholders
Dime Bancorp, Inc.:

         We have audited the accompanying consolidated statements of financial
condition of Dime Bancorp, Inc. and subsidiaries (Dime) as of December 31, 1999
and 1998, and the related consolidated statements of income, changes in
stockholders' equity, cash flows and comprehensive income for each of the years
in the three-year period ended December 31, 1999. These consolidated financial
statements are the responsibility of Dime's management. Our responsibility is to
express an opinion on these consolidated financial statements based on our
audits.

         We conducted our audits in accordance with generally accepted auditing
standards. Those standards require that we plan and perform the audit to obtain
reasonable assurance about whether the financial statements are free of material
misstatement. An audit includes examining, on a test basis, evidence supporting
the amounts and disclosures in the financial statements. An audit also includes
assessing the accounting principles used and significant estimates made by
management, as well as evaluating the overall financial statement presentation.
We believe that our audits provide a reasonable basis for our opinion.

         In our opinion, the consolidated financial statements referred to above
present fairly, in all material respects, the financial position of Dime
Bancorp, Inc. and subsidiaries as of December 31, 1999 and 1998, and the results
of their operations and their cash flows for each of the years in the three-year
period ended December 31, 1999, in conformity with generally accepted accounting
principles.


/s/ KPMG LLP

New York, New York
January 20, 2000, EXCEPT FOR NOTE 23 AND NOTE 28, WHICH ARE AS OF MARCH 23, 2000
<PAGE>   3
                       DIME BANCORP, INC. AND SUBSIDIARIES

            NOTES TO CONSOLIDATED FINANCIAL STATEMENTS -- (Continued)

Note 28 - Subsequent Events

         On February 10, 2000, the Holding Company and Hudson mailed a joint
proxy statement/prospectus, dated February 9, 2000, to their respective
stockholders. This document notified stockholders that each of the Holding
Company and Hudson intended to hold special stockholders meetings on March 15,
2000 to consider approval of the Merger.

         On March 5, 2000, North Fork announced its intention to make a hostile
bid to acquire all of the outstanding shares of Common Stock and to terminate
the Merger. On March 6, 2000, North Fork filed preliminary proxy materials with
the Securities and Exchange Commission with which it proposed to solicit proxies
to vote against the Merger.

         On March 8, 2000, the Holding Company mailed to its stockholders a
supplement to the February 9, 2000 joint proxy statement/prospectus stating,
among other things, its recommendation that Dime Stockholders not tender shares
of Common Stock in North Fork's offer, if and when it commenced. On March 9,
2000, the Holding Company and Hudson announced that they were both voluntarily
postponing their respective special stockholders meetings until March 24, 2000
in order to allow information to be disseminated.

         On March 13, 2000, North Fork mailed definitive proxy solicitation
materials to Dime Stockholders in order to solicit proxies against the Merger.
On March 15, 2000, North Fork formally commenced the Exchange Offer. Pursuant to
the terms of the Exchange Offer, Dime Stockholders would receive 0.9302 shares
of North Fork's common stock and $2.00 in cash for each share of Common Stock
tendered to North Fork. The Exchange Offer is conditioned on the satisfaction of
a number of factors, including, but not limited to: (i) termination of the
Merger Agreement; (ii) the Holding Company entering into a merger agreement with
North Fork; (iii) receipt of required regulatory approvals; and (iv) the rights
under the Stockholder Protection Rights Plan, dated as of October 20, 1995,
between the Holding Company and The First National Bank of Boston, as rights
agent, not being applicable. On March 20, 2000, the Board formally recommended
that Dime Stockholders reject the Exchange Offer by not tendering Common Stock
to North Fork. On that date, the Holding Company and Hudson postponed their
respective special stockholders meetings to May 17, 2000 and May 18, 2000,
respectively. On March 23, 2000, North Fork extended the expiration date of the
Exchange Offer from April 14, 2000 to midnight on May 31, 2000.

         On March 10, 2000, the Holding Company filed suit in the Supreme Court
of the State of New York, County of New York, against North Fork and Fleet
Boston Corporation ("Fleet Boston"). The complaint alleges violations of New
York's antitrust laws, including a conspiracy between North Fork and Fleet
Boston to: (i) diminish competition in a variety of banking markets; (ii)
diminish competition for the purchase of banks and thrifts in some markets; and
(iii) eliminate a stronger competitor (i.e., the combined institution resulting
from the Merger). In addition, the complaint alleges that Fleet Boston's
divestiture of branches from the Fleet Financial-BankBoston Corporation merger
to Sovereign Bancorp, Inc. ("Sovereign") is part of the conspiracy, as Sovereign
is not capable of competing effectively in markets with Fleet Boston and Fleet
Boston may use monopoly profits gained in those markets to fund the Exchange
Offer. The suit asks the court to: (i) enjoin North Fork and Fleet Boston from
acting in concert to acquire the Holding Company or otherwise interfere with the
Merger; (ii) enjoin the proposed branch divestiture from Fleet Boston to
Sovereign and require divestiture to a banking organization with a reasonable
opportunity to improve competition in the markets served; and (iii) declare
violations of the New York antitrust laws.

         On March 13, 2000, North Fork filed a motion in the Delaware Court of
Chancery to enjoin prosecution of the action filed by the Holding Company in New
York County, alleging that such action must be brought as counterclaims in North
Fork's lawsuit in the Delaware Court of Chancery. On March 17,
<PAGE>   4
2000, the Holding Company filed a response opposing this motion. On March 20,
2000, the Delaware Court of Chancery refused to enjoin the Holding Company from
prosecuting its antitrust claims in the New York courts. The Holding Company
intends to proceed vigorously with this prosecution.

         On March 21, 2000, the Holding Company filed suit in the United States
District Court for the Eastern District of New York against North Fork and
members of North Fork's board of directors seeking preliminary and permanent
injunctive relief in connection with alleged misrepresentations contained in
North Fork's proxy statement, dated March 13, 2000, soliciting proxies against
the Merger, in violation of the Securities Exchange Act of 1934.

         For a discussion of various litigation against the Company in
connection with the Exchange Offer and the Merger, see Note 23, "Commitments and
Contingent Liabilities."
<PAGE>   5
                                   SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the
Registrant has duly caused this report to be signed on its behalf by the
undersigned thereunto duly authorized.


                                            DIME BANCORP, INC.


Dated: March 30, 2000                       By:  /s/ Anthony R. Burriesci
                                                 ------------------------------
                                                 Anthony R. Burriesci
                                                 Chief Financial Officer
                                                 (Principal Financial Officer)
<PAGE>   6
                                  EXHIBIT INDEX


<TABLE>
<CAPTION>
                                                          Sequentially
Exhibit No.                                               Numbered Page
-----------                                               -------------
<S>                                                       <C>
23       Consent of KPMG LLP                                    7

</TABLE>