SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549


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                                    FORM 8-K

                                 CURRENT REPORT
                     PURSUANT TO SECTION 13 OR 15(d) OF THE
                         SECURITIES EXCHANGE ACT OF 1934




                Date of Report (Date of earliest event reported):
                     December 31, 1997 (December 17, 1997)




                                SIS Bancorp, Inc.
               (Exact name of registrant as specified in charter)




      Massachusetts                   000-20809                   04-3303264
(State or other jurisdiction    (Commission file number)       (IRS employer 
     of incorporation)                                       identification no.)

   1441 Main Street, Springfield, MA                                01102
(Address of principal executive offices)                          (Zip code)

                                 (413) 748-8000
               Registrant's telephone number, including area code




Item 2. ACQUISITION OR DISPOSITION OF ASSETS

         On December 17, 1997, SIS Bancorp,  Inc.  ("SIS")  completed its merger
(the "Merger") with  Glastonbury  Bank & Trust Company  ("GBT"),  pursuant to an
Agreement  and Plan of  Reorganization  dated as of August 18, 1997 (the "Merger
Agreement")  by and  between SIS and GBT.  In  accordance  with the terms of the
Merger  Agreement,  a wholly owned  subsidiary  of SIS merged with and into GBT,
which then became a wholly  owned  subsidiary  of SIS.  Each share of GBT common
stock, par value $2.50 per share,  outstanding  immediately  prior to the Merger
was converted  into the right to receive  74/100ths  (0.74) of a share of common
stock of SIS, par value $.01 per share.

         The Merger  constitutes a tax-free  reorganization  and no gain or loss
will be recognized  by SIS or GBT as a result of the Merger.  The Merger will be
accounted for as a "pooling of interests" transaction.

         Certain  additional  information  regarding  the Merger is contained in
SIS's press release  dated  December 18, 1997, a copy of which is included as an
exhibit hereto and incorporated herein.

Item 7. FINANCIAL STATEMENTS AND EXHIBITS

(c)      Exhibits.

         99.1     Press Release of SIS, dated December 18, 1997








                                   SIGNATURES

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


                                SIS BANCORP, INC.


Date: December 31, 1997        By: /s/ John F. Treanor
                                   Name: John F. Treanor
                                   Title:  Executive Vice President, Chief 
                                             Financial Officer and Treasurer