<TABLE> <S> <C>



<ARTICLE>                                            9
<LEGEND>
This  schedule  contains  summary  financial   information  extracted  from  the
unaudited financial statements of SIS Bancorp,  Inc. at and for the period ended
September  30,  1997 and is  qualified  in its  entirety  by  reference  to such
financial statements.
</LEGEND>
<MULTIPLIER>                                   1,000
       
<S>                             <C>
<PERIOD-TYPE>                   9-Mos
<FISCAL-YEAR-END>                              Dec-31-1997
<PERIOD-START>                                 Jan-01-1997
<PERIOD-END>                                   Sep-30-1997
<CASH>                                         34,464
<INT-BEARING-DEPOSITS>                         6,692
<FED-FUNDS-SOLD>                               0
<TRADING-ASSETS>                               0
<INVESTMENTS-HELD-FOR-SALE>                    502,868
<INVESTMENTS-CARRYING>                         182,320
<INVESTMENTS-MARKET>                           182,537
<LOANS>                                        670,056
<ALLOWANCE>                                    18,393
<TOTAL-ASSETS>                                 1,453,017
<DEPOSITS>                                     1,021,613
<SHORT-TERM>                                   283,185
<LIABILITIES-OTHER>                            38,591
<LONG-TERM>                                    2,670
<PREFERRED-MANDATORY>                          0
<PREFERRED>                                    0
<COMMON>                                       57
<OTHER-SE>                                     106,901
<TOTAL-LIABILITIES-AND-EQUITY>                 1,453,017
<INTEREST-LOAN>                                40,285
<INTEREST-INVEST>                              33,954
<INTEREST-OTHER>                               716
<INTEREST-TOTAL>                               74,955
<INTEREST-DEPOSIT>                             25,614
<INTEREST-EXPENSE>                             37,396
<INTEREST-INCOME-NET>                          37,559
<LOAN-LOSSES>                                  1,203
<SECURITIES-GAINS>                             21
<EXPENSE-OTHER>                                10,992
<INCOME-PRETAX>                                14,660
<INCOME-PRE-EXTRAORDINARY>                     14,660
<EXTRAORDINARY>                                0
<CHANGES>                                      0
<NET-INCOME>                                   8,929
<EPS-PRIMARY>                                  1.60
<EPS-DILUTED>                                  1.58
<YIELD-ACTUAL>                                 3.79
<LOANS-NON>                                    4,058
<LOANS-PAST>                                   121
<LOANS-TROUBLED>                               475
<LOANS-PROBLEM>                                9,060
<ALLOWANCE-OPEN>                               15,597
<CHARGE-OFFS>                                  1,612
<RECOVERIES>                                   3,205
<ALLOWANCE-CLOSE>                              18,393
<ALLOWANCE-DOMESTIC>                           18,393
<ALLOWANCE-FOREIGN>                            0
<ALLOWANCE-UNALLOCATED>                        0
        

</TABLE>