WARNING: THE EDGAR SYSTEM ENCOUNTERED ERROR(S) WHILE PROCESSING THIS SCHEDULE.
<TABLE> <S> <C>
<ARTICLE> 6
<CIK> 0000781880
<NAME> LEGG MASON SPECIAL INVESTMENT TRUST, INC. - PRIMARY SHARES
<MULTIPLIER> 1000
<S> <C>
<PERIOD-TYPE> 6-MOS
<FISCAL-YEAR-END> MAR-31-2001
<PERIOD-START> APR-01-2000
<PERIOD-END> SEP-30-2000
<INVESTMENTS-AT-COST> 1912818
<INVESTMENTS-AT-VALUE> 2626905
<RECEIVABLES> 10753
<ASSETS-OTHER> 37
<OTHER-ITEMS-ASSETS> 0
<TOTAL-ASSETS> 2637695
<PAYABLE-FOR-SECURITIES> 3075
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 5526
<TOTAL-LIABILITIES> 8601
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 1734064
<SHARES-COMMON-STOCK> 67628
<SHARES-COMMON-PRIOR> 65791
<ACCUMULATED-NII-CURRENT> (12262)
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> 105639
<OVERDISTRIBUTION-GAINS> 0
<ACCUM-APPREC-OR-DEPREC> 714086
<NET-ASSETS> 2629094
<DIVIDEND-INCOME> 5765
<INTEREST-INCOME> 5046
<OTHER-INCOME> 0
<EXPENSES-NET> 23073
<NET-INVESTMENT-INCOME> (12262)
<REALIZED-GAINS-CURRENT> 105629
<APPREC-INCREASE-CURRENT> (210086)
<NET-CHANGE-FROM-OPS> (116719)
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> 0
<DISTRIBUTIONS-OF-GAINS> (99878)
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 3609
<NUMBER-OF-SHARES-REDEEMED> (4411)
<SHARES-REINVESTED> 2639
<NET-CHANGE-IN-ASSETS> (142844)
<ACCUMULATED-NII-PRIOR> (26885)
<ACCUMULATED-GAINS-PRIOR> 116003
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 9234
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 23100
<AVERAGE-NET-ASSETS> 2519597
<PER-SHARE-NAV-BEGIN> 40.28
<PER-SHARE-NII> (.18)
<PER-SHARE-GAIN-APPREC> (1.54)
<PER-SHARE-DIVIDEND> 0
<PER-SHARE-DISTRIBUTIONS> (1.52)
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 37.04
<EXPENSE-RATIO> 1.79
</TABLE>