<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,  1998 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-31-1998
<PERIOD-START>                                 JAN-01-1998
<PERIOD-END>                                   SEP-30-1998
<CASH>                                         37,225
<INT-BEARING-DEPOSITS>                         25,242
<FED-FUNDS-SOLD>                               27,000
<TRADING-ASSETS>                               0
<INVESTMENTS-HELD-FOR-SALE>                    619,420
<INVESTMENTS-CARRYING>                         244,238
<INVESTMENTS-MARKET>                           245,202
<LOANS>                                        875,250
<ALLOWANCE>                                    23,924
<TOTAL-ASSETS>                                 1,900,418
<DEPOSITS>                                     1,343,063
<SHORT-TERM>                                   378,316
<LIABILITIES-OTHER>                            37,605
<LONG-TERM>                                    2,294
<PREFERRED-MANDATORY>                          0
<PREFERRED>                                    0
<COMMON>                                       72
<OTHER-SE>                                     139,068
<TOTAL-LIABILITIES-AND-EQUITY>                 1,900,418
<INTEREST-LOAN>                                54,963
<INTEREST-INVEST>                              37,098
<INTEREST-OTHER>                               1,596
<INTEREST-TOTAL>                               93,657
<INTEREST-DEPOSIT>                             32,834
<INTEREST-EXPENSE>                             47,027
<INTEREST-INCOME-NET>                          46,630
<LOAN-LOSSES>                                  755
<SECURITIES-GAINS>                             3
<EXPENSE-OTHER>                                38,119
<INCOME-PRETAX>                                20,804
<INCOME-PRE-EXTRAORDINARY>                     20,804
<EXTRAORDINARY>                                0
<CHANGES>                                      0
<NET-INCOME>                                   12,899
<EPS-PRIMARY>                                  1.89
<EPS-DILUTED>                                  1.79
<YIELD-ACTUAL>                                 7.39
<LOANS-NON>                                    3,677
<LOANS-PAST>                                   371
<LOANS-TROUBLED>                               275
<LOANS-PROBLEM>                                17,190
<ALLOWANCE-OPEN>                               22,724
<CHARGE-OFFS>                                  1,298
<RECOVERIES>                                   1,743
<ALLOWANCE-CLOSE>                              23,924
<ALLOWANCE-DOMESTIC>                           23,924
<ALLOWANCE-FOREIGN>                            0
<ALLOWANCE-UNALLOCATED>                        0
        


</TABLE>