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                                                                     Exhibit 5.1


              [Letterhead of Patterson, Belknap, Webb & Tyler LLP]

                                  June 13, 2001


Dime Bancorp, Inc.
589 Fifth Avenue
New York, New York  10017

Dear Sirs:

                  As set forth in the Registration Statement on Form S-8
("Registration Statement") proposed to be filed by Dime Bancorp, Inc. (the
"Company") on June 13, 2001 under the Securities Act of 1933, as amended,
relating to 2,600,000 shares (the "Shares") of common stock, par value $.01 per
share, of the Company to be issued pursuant to the Dime Bancorp, Inc. Stock
Incentive Plan and Dime Bancorp, Inc. 1991 Stock Incentive Plan (collectively,
the "Plan"), certain legal matters in connection with the Shares offered
pursuant to the Plan are being passed upon for the Company by this firm. At your
request, this opinion of counsel is being furnished to you for filing with the
Registration Statement.

                  In our capacity as counsel in this connection, we have
familiarized ourselves with the Amended and Restated Certificate of
Incorporation and Bylaws, each as amended to date, of the Company and have
examined the originals, or copies certified or otherwise identified, of the
Plan, corporate records of the Company, certificates of public officials and
representatives of the Company, statutes and other instruments and documents as
the basis for the opinion hereinafter expressed.

                On the basis of the foregoing, we are of the opinion that the
Shares, when issued and sold pursuant to the provisions of the Plan for a
consideration at least equal to the par value of the shares, will be duly
authorized, validly issued, fully paid and nonassessable.

                We hereby consent to the filing of this opinion letter with
the Registration Statement.

                                         PATTERSON, BELKBAP, WEBB & TYLER LLP

                                         BY: /S/ Jeffrey E. LaGueux
                                             ----------------------------------
                                             Jeffrey E. LaGueux