<TABLE> <S> <C>

<ARTICLE> 6
<LEGEND>
THIS SCHEDULE CONTAINS SUMMARY FINANCIAL INFORMATION EXTRACTED FROM THE JOHN
HANCOCK VARIABLE SERIES TRUST I ANNUAL REPORT DATED DECEMBER 31, 1998 AND IS
QUALIFIED IN ITS ENTIRETY BY REFERENCE TO SUCH FINANCIAL STATEMENTS.
</LEGEND>
<SERIES>
   <NUMBER> 12
   <NAME> MID CAP GROWTH
<MULTIPLIER> 1000
       
<S>                             <C>
<PERIOD-TYPE>                   YEAR
<FISCAL-YEAR-END>                          DEC-31-1998
<PERIOD-START>                             JAN-01-1998
<PERIOD-END>                               DEC-31-1998
<INVESTMENTS-AT-COST>                           68,410
<INVESTMENTS-AT-VALUE>                          92,304
<RECEIVABLES>                                    3,127
<ASSETS-OTHER>                                     533
<OTHER-ITEMS-ASSETS>                                 0
<TOTAL-ASSETS>                                  95,964
<PAYABLE-FOR-SECURITIES>                         1,862
<SENIOR-LONG-TERM-DEBT>                              0
<OTHER-ITEMS-LIABILITIES>                           17
<TOTAL-LIABILITIES>                              1,879
<SENIOR-EQUITY>                                      0
<PAID-IN-CAPITAL-COMMON>                        72,467
<SHARES-COMMON-STOCK>                            6,224
<SHARES-COMMON-PRIOR>                                0
<ACCUMULATED-NII-CURRENT>                         (69)
<OVERDISTRIBUTION-NII>                               0
<ACCUMULATED-NET-GAINS>                          (141)
<OVERDISTRIBUTION-GAINS>                             0
<ACCUM-APPREC-OR-DEPREC>                        21,795
<NET-ASSETS>                                    94,085
<DIVIDEND-INCOME>                                  134
<INTEREST-INCOME>                                  138
<OTHER-INCOME>                                       0
<EXPENSES-NET>                                     655
<NET-INVESTMENT-INCOME>                          (383)
<REALIZED-GAINS-CURRENT>                         8,102
<APPREC-INCREASE-CURRENT>                       15,616
<NET-CHANGE-FROM-OPS>                           23,335
<EQUALIZATION>                                       0
<DISTRIBUTIONS-OF-INCOME>                            0
<DISTRIBUTIONS-OF-GAINS>                       (7,468)
<DISTRIBUTIONS-OTHER>                            (833)
<NUMBER-OF-SHARES-SOLD>                          3,075
<NUMBER-OF-SHARES-REDEEMED>                      (774)
<SHARES-REINVESTED>                                549
<NET-CHANGE-IN-ASSETS>                          83,850
<ACCUMULATED-NII-PRIOR>                              0
<ACCUMULATED-GAINS-PRIOR>                            0
<OVERDISTRIB-NII-PRIOR>                              0
<OVERDIST-NET-GAINS-PRIOR>                           0
<GROSS-ADVISORY-FEES>                              507
<INTEREST-EXPENSE>                                   0
<GROSS-EXPENSE>                                    670
<AVERAGE-NET-ASSETS>                            59,636
<PER-SHARE-NAV-BEGIN>                            11.93
<PER-SHARE-NII>                                 (0.09)
<PER-SHARE-GAIN-APPREC>                           4.75
<PER-SHARE-DIVIDEND>                                 0
<PER-SHARE-DISTRIBUTIONS>                       (1.32)
<RETURNS-OF-CAPITAL>                            (0.15)
<PER-SHARE-NAV-END>                              15.12
<EXPENSE-RATIO>                                   1.10
<AVG-DEBT-OUTSTANDING>                               0
<AVG-DEBT-PER-SHARE>                                 0
        

</TABLE>