<PAGE> PAGE 1
000 B000000 09/30/98
000 C000000 0000912492
000 D000000 N
000 E000000 NF
000 F000000 Y
000 G000000 N
000 H000000 N
000 I000000 3.0.a
000 J000000 U
001 A000000 DREYFUS INSTITUTIONAL SHORT TERM TREAS FUND
001 B000000 811-07097
001 C000000 2129226764
002 A000000 200 PARK AVENUE
002 B000000 NEW YORK
002 C000000 NY
002 D010000 10166
003 000000 N
004 000000 N
005 000000 N
006 000000 N
007 A000000 N
007 B000000 0
018 000000 Y
019 A000000 Y
019 B000000 165
019 C000000 DREYFUSFAM
022 A000001 AUBREY G. LANSTON & CO. INC.
022 B000001 13-5552129
022 C000001 1192929
022 D000001 0
022 A000002 MERRILL LYNCH, PIERCE, FENNER & SMITH INC.
022 B000002 13-5674085
022 C000002 526573
022 D000002 530174
022 A000003 BARCLAY DE ZOETE WEDD SECURITIES, INC.
022 B000003 13-3551367
022 C000003 728667
022 D000003 0
022 A000004 UBS AG
022 B000004 13-2932996
022 C000004 504114
022 D000004 0
022 A000005 GOLDMAN, SACHS & CO.
022 B000005 13-5108880
022 C000005 131283
022 D000005 103802
022 A000006 DEUTSCHE BANK SECURITIES CORPORATION
022 B000006 13-2730828
022 C000006 93693
022 D000006 110464
022 A000007 GREENWICH PARTNERS, INC.
<PAGE> PAGE 2
022 B000007 13-3176013
022 C000007 86739
022 D000007 96900
022 A000008 LEHMAN BROTHERS INC.
022 B000008 13-2518466
022 C000008 159404
022 D000008 0
022 A000009 CS FIRST BOSTON CORPORATION
022 B000009 13-5659485
022 C000009 23639
022 D000009 34798
022 A000010 ARBOR TRADING GROUP, INC.
022 B000010 36-3540782
022 C000010 19911
022 D000010 20090
023 C000000 3536934
023 D000000 978987
025 A000001 UBS AG
025 B000001 13-2932996
025 C000001 D
025 D000001 185
025 D000002 0
025 D000003 0
025 D000004 0
025 D000005 0
025 D000006 0
025 D000007 0
025 D000008 0
027 000000 Y
028 A010000 2082
028 A020000 366
028 A030000 0
028 A040000 9290
028 B010000 1203
028 B020000 311
028 B030000 0
028 B040000 13930
028 C010000 1779
028 C020000 344
028 C030000 0
028 C040000 3985
028 D010000 1153
028 D020000 310
028 D030000 0
028 D040000 6334
028 E010000 2986
028 E020000 297
028 E030000 0
028 E040000 25056
028 F010000 715
028 F020000 196
<PAGE> PAGE 3
028 F030000 0
028 F040000 5865
028 G010000 9918
028 G020000 1824
028 G030000 0
028 G040000 64460
028 H000000 0
029 000000 N
030 A000000 0
030 B000000 0.00
030 C000000 0.00
042 A000000 1
042 B000000 0
042 C000000 99
042 D000000 0
042 E000000 0
042 F000000 0
042 G000000 0
042 H000000 0
043 000000 63
044 000000 0
054 A000000 Y
054 B000000 Y
054 C000000 Y
054 D000000 N
054 E000000 N
054 F000000 N
054 G000000 Y
054 H000000 N
054 I000000 N
054 J000000 Y
054 K000000 N
054 L000000 Y
054 M000000 Y
054 N000000 N
054 O000000 Y
055 A000000 Y
055 B000000 N
056 000000 N
057 000000 N
062 A000000 Y
062 B000000 0.0
062 C000000 0.0
062 D000000 0.3
062 E000000 0.0
062 F000000 0.0
062 G000000 0.0
062 H000000 0.0
062 I000000 0.0
062 J000000 0.0
062 K000000 0.0
<PAGE> PAGE 4
062 L000000 0.0
062 M000000 98.5
062 N000000 0.0
062 O000000 0.0
062 P000000 0.0
062 Q000000 0.0
062 R000000 0.0
063 A000000 0
063 B000000 2.0
064 A000000 Y
064 B000000 N
066 A000000 N
067 000000 N
068 A000000 N
068 B000000 N
069 000000 N
070 A010000 Y
070 A020000 Y
070 B010000 N
070 B020000 N
070 C010000 N
070 C020000 N
070 D010000 N
070 D020000 N
070 E010000 N
070 E020000 N
070 F010000 N
070 F020000 N
070 G010000 N
070 G020000 N
070 H010000 N
070 H020000 N
070 I010000 N
070 I020000 N
070 J010000 N
070 J020000 N
070 K010000 Y
070 K020000 N
070 L010000 N
070 L020000 N
070 M010000 N
070 M020000 N
070 N010000 Y
070 N020000 N
070 O010000 Y
070 O020000 Y
070 P010000 Y
070 P020000 N
070 Q010000 N
070 Q020000 N
070 R010000 N
<PAGE> PAGE 5
070 R020000 N
071 A000000 902492
071 B000000 978987
071 C000000 119298
071 D000000 757
072 A000000 12
072 B000000 7633
072 C000000 0
072 D000000 0
072 E000000 0
072 F000000 254
072 G000000 0
072 H000000 0
072 I000000 0
072 J000000 0
072 K000000 0
072 L000000 0
072 M000000 0
072 N000000 0
072 O000000 0
072 P000000 2
072 Q000000 0
072 R000000 0
072 S000000 0
072 T000000 63
072 U000000 0
072 V000000 0
072 W000000 0
072 X000000 319
072 Y000000 0
072 Z000000 7314
072AA000000 1611
072BB000000 876
072CC010000 741
072CC020000 0
072DD010000 1404
072DD020000 5910
072EE000000 0
073 A010000 0.1150
073 A020000 0.1108
073 B000000 0.0000
073 C000000 0.0000
074 A000000 0
074 B000000 185
074 C000000 0
074 D000000 74347
074 E000000 0
074 F000000 0
074 G000000 0
074 H000000 0
074 I000000 0
<PAGE> PAGE 6
074 J000000 9995
074 K000000 0
074 L000000 950
074 M000000 0
074 N000000 85477
074 O000000 0
074 P000000 13
074 Q000000 0
074 R010000 0
074 R020000 0
074 R030000 0
074 R040000 10005
074 S000000 0
074 T000000 75459
074 U010000 32408
074 U020000 5087
074 V010000 2.01
074 V020000 2.02
074 W000000 0.0000
074 X000000 106
074 Y000000 0
075 A000000 101643
075 B000000 0
076 000000 0.00
077 A000000 Y
077 B000000 Y
080 A000000 VIGILANT INSURANCE COMPANY
080 B000000 NATIONAL UNION FIRE INSURANCE COMPANY
080 C000000 125000
081 A000000 Y
081 B000000 165
082 A000000 N
082 B000000 0
083 A000000 N
083 B000000 0
084 A000000 N
084 B000000 0
085 A000000 Y
085 B000000 N
SIGNATURE MICHAEL S. PETRUCELLI
TITLE V.P & ASST TREASURER
<TABLE> <S> <C>
<ARTICLE> 6
<CIK> 0000912492
<NAME> DREYFUS INSTITUTIONAL SHORT TERM TREASURY FUND
<SERIES>
<NUMBER> 001
<NAME> INSTITUTIONAL SHARES
<MULTIPLIER> 1000
<S> <C>
<PERIOD-TYPE> 12-MOS
<FISCAL-YEAR-END> SEP-30-1998
<PERIOD-END> SEP-30-1998
<INVESTMENTS-AT-COST> 73649
<INVESTMENTS-AT-VALUE> 74532
<RECEIVABLES> 10945
<ASSETS-OTHER> 0
<OTHER-ITEMS-ASSETS> 0
<TOTAL-ASSETS> 85477
<PAYABLE-FOR-SECURITIES> 0
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 10018
<TOTAL-LIABILITIES> 10018
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 77387
<SHARES-COMMON-STOCK> 32408
<SHARES-COMMON-PRIOR> 59670
<ACCUMULATED-NII-CURRENT> 0
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> (2811)
<OVERDISTRIBUTION-GAINS> 0
<ACCUM-APPREC-OR-DEPREC> 883
<NET-ASSETS> 65163
<DIVIDEND-INCOME> 0
<INTEREST-INCOME> 7633
<OTHER-INCOME> 0
<EXPENSES-NET> 319
<NET-INVESTMENT-INCOME> 7314
<REALIZED-GAINS-CURRENT> 735
<APPREC-INCREASE-CURRENT> 741
<NET-CHANGE-FROM-OPS> 8790
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> (1404)
<DISTRIBUTIONS-OF-GAINS> 0
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 10749
<NUMBER-OF-SHARES-REDEEMED> (39942)
<SHARES-REINVESTED> 1932
<NET-CHANGE-IN-ASSETS> (77939)
<ACCUMULATED-NII-PRIOR> 0
<ACCUMULATED-GAINS-PRIOR> (3547)
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 254
<INTEREST-EXPENSE> 2
<GROSS-EXPENSE> 319
<AVERAGE-NET-ASSETS> 101643
<PER-SHARE-NAV-BEGIN> 1.98
<PER-SHARE-NII> .12
<PER-SHARE-GAIN-APPREC> 0.03
<PER-SHARE-DIVIDEND> (.12)
<PER-SHARE-DISTRIBUTIONS> 0
<RETURNS-OF-CAPITAL> .000
<PER-SHARE-NAV-END> 2.01
<EXPENSE-RATIO> .002
<AVG-DEBT-OUTSTANDING> 0
<AVG-DEBT-PER-SHARE> 0
</TABLE>
<TABLE> <S> <C>
<ARTICLE> 6
<CIK> 0000912492
<NAME> DREYFUS INSTITUTIONAL SHORT TERM TREASURY FUND
<SERIES>
<NUMBER> 002
<NAME> INVESTOR SHARES
<MULTIPLIER> 1000
<S> <C>
<PERIOD-TYPE> 12-MOS
<FISCAL-YEAR-END> SEP-30-1998
<PERIOD-END> SEP-30-1998
<INVESTMENTS-AT-COST> 73649
<INVESTMENTS-AT-VALUE> 74532
<RECEIVABLES> 10945
<ASSETS-OTHER> 0
<OTHER-ITEMS-ASSETS> 0
<TOTAL-ASSETS> 85477
<PAYABLE-FOR-SECURITIES> 0
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 10018
<TOTAL-LIABILITIES> 10018
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 77387
<SHARES-COMMON-STOCK> 5087
<SHARES-COMMON-PRIOR> 17716
<ACCUMULATED-NII-CURRENT> 0
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> (2811)
<OVERDISTRIBUTION-GAINS> 0
<ACCUM-APPREC-OR-DEPREC> 883
<NET-ASSETS> 10296
<DIVIDEND-INCOME> 0
<INTEREST-INCOME> 7633
<OTHER-INCOME> 0
<EXPENSES-NET> 319
<NET-INVESTMENT-INCOME> 7314
<REALIZED-GAINS-CURRENT> 735
<APPREC-INCREASE-CURRENT> 741
<NET-CHANGE-FROM-OPS> 8790
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> (5910)
<DISTRIBUTIONS-OF-GAINS> 0
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 12870
<NUMBER-OF-SHARES-REDEEMED> (26074)
<SHARES-REINVESTED> 575
<NET-CHANGE-IN-ASSETS> (77939)
<ACCUMULATED-NII-PRIOR> 0
<ACCUMULATED-GAINS-PRIOR> (3547)
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 254
<INTEREST-EXPENSE> 2
<GROSS-EXPENSE> 319
<AVERAGE-NET-ASSETS> 25212
<PER-SHARE-NAV-BEGIN> 1.99
<PER-SHARE-NII> .11
<PER-SHARE-GAIN-APPREC> 0.03
<PER-SHARE-DIVIDEND> (.11)
<PER-SHARE-DISTRIBUTIONS> 0
<RETURNS-OF-CAPITAL> .000
<PER-SHARE-NAV-END> 2.02
<EXPENSE-RATIO> .005
<AVG-DEBT-OUTSTANDING> 0
<AVG-DEBT-PER-SHARE> 0
</TABLE>