<TABLE> <S> <C>

<ARTICLE> 6
<LEGEND>
THIS SCHEDULE CONTAINS SUMMARY FINANCIAL INFORMATION EXTRACTED FROM THE JOHN
HANCOCK VARIABLE SERIES TRUST I SEMIANNUAL REPORT DATED JUNE 30, 1999 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>                   6-MOS
<FISCAL-YEAR-END>                          DEC-31-1999
<PERIOD-START>                             JAN-01-1999
<PERIOD-END>                               JUN-30-1999
<INVESTMENTS-AT-COST>                          136,118
<INVESTMENTS-AT-VALUE>                         184,885
<RECEIVABLES>                                    2,532
<ASSETS-OTHER>                                      21
<OTHER-ITEMS-ASSETS>                                 0
<TOTAL-ASSETS>                                 187,438
<PAYABLE-FOR-SECURITIES>                         5,911
<SENIOR-LONG-TERM-DEBT>                              0
<OTHER-ITEMS-LIABILITIES>                           30
<TOTAL-LIABILITIES>                              5,941
<SENIOR-EQUITY>                                      0
<PAID-IN-CAPITAL-COMMON>                       128,703
<SHARES-COMMON-STOCK>                            9,452
<SHARES-COMMON-PRIOR>                                0
<ACCUMULATED-NII-CURRENT>                        (485)
<OVERDISTRIBUTION-NII>                               0
<ACCUMULATED-NET-GAINS>                         14,812
<OVERDISTRIBUTION-GAINS>                             0
<ACCUM-APPREC-OR-DEPREC>                        38,467
<NET-ASSETS>                                   181,497
<DIVIDEND-INCOME>                                   62
<INTEREST-INCOME>                                  141
<OTHER-INCOME>                                       0
<EXPENSES-NET>                                     619
<NET-INVESTMENT-INCOME>                          (416)
<REALIZED-GAINS-CURRENT>                        14,812
<APPREC-INCREASE-CURRENT>                       16,639
<NET-CHANGE-FROM-OPS>                           31,035
<EQUALIZATION>                                       0
<DISTRIBUTIONS-OF-INCOME>                            0
<DISTRIBUTIONS-OF-GAINS>                             0
<DISTRIBUTIONS-OTHER>                                0
<NUMBER-OF-SHARES-SOLD>                          3,816
<NUMBER-OF-SHARES-REDEEMED>                      (588)
<SHARES-REINVESTED>                                  0
<NET-CHANGE-IN-ASSETS>                          87,412
<ACCUMULATED-NII-PRIOR>                              0
<ACCUMULATED-GAINS-PRIOR>                            0
<OVERDISTRIB-NII-PRIOR>                              0
<OVERDIST-NET-GAINS-PRIOR>                           0
<GROSS-ADVISORY-FEES>                              544
<INTEREST-EXPENSE>                                   0
<GROSS-EXPENSE>                                    619
<AVERAGE-NET-ASSETS>                                 0
<PER-SHARE-NAV-BEGIN>                            15.12
<PER-SHARE-NII>                                  (.17)
<PER-SHARE-GAIN-APPREC>                           4.25
<PER-SHARE-DIVIDEND>                                 0
<PER-SHARE-DISTRIBUTIONS>                            0
<RETURNS-OF-CAPITAL>                                 0
<PER-SHARE-NAV-END>                              19.20
<EXPENSE-RATIO>                                    .95


</TABLE>