<PAGE> PAGE 1
000 B000000 12/31/97
000 C000000 315783
000 D000000 N
000 E000000 NF
000 F000000 Y
000 G000000 N
000 H000000 N
000 I000000 3.0
000 J000000 U
001 A000000 DREYFUS INSTITUTIONAL MONEY MARKET FUND
001 B000000 811-3025
001 C000000 2129226775
002 A000000 144 GLENN CURTISS BOULEVARD
002 B000000 UNIONDALE
002 C000000 NY
002 D010000 11556
002 D020000 0144
003 000000 N
004 000000 N
005 000000 N
006 000000 N
007 A000000 Y
007 B000000 2
007 C010100 1
007 C020100 MONEY MARKET SERIES
007 C030100 N
007 C010200 2
007 C020200 GOVERNMENT SECURITIES SERIES
007 C030200 N
007 C010300 3
007 C010400 4
007 C010500 5
007 C010600 6
007 C010700 7
007 C010800 8
007 C010900 9
007 C011000 10
015 A00AA01 THE BANK OF NEW YORK
015 B00AA01 C
015 C01AA01 NEW YORK
015 C02AA01 NY
015 C03AA01 10286
015 E01AA01 X
015 A00AA02 DELETE
018 00AA00 Y
019 A00AA00 Y
019 B00AA00 151
019 C00AA00 DREYFUSFAM
022 A000001 UBS SECURITIES INC.
022 B000001 13-2932996
022 C000001 7053718
<PAGE> PAGE 2
022 D000001 154273
022 A000002 AUBREY G. LANSTON & CO. INC.
022 B000002 13-5552129
022 C000002 6081828
022 D000002 24890
022 A000003 SBC CAPITAL MARKETS, INC.
022 B000003 13-3498485
022 C000003 4396918
022 D000003 0
022 A000004 BARCLAYS DE ZOETE WEDD SECURITIES, INC.
022 B000004 13-3551367
022 C000004 2759205
022 D000004 19881
022 A000005 REPUBLIC NATIONAL BANK OF NEW YORK
022 B000005 13-2774727
022 C000005 2537519
022 D000005 0
022 A000006 BEAR, STEARNS & CO. INC.
022 B000006 13-3299429
022 C000006 2461386
022 D000006 0
022 A000007 DAIWA SECURITIES AMERICA INC.
022 B000007 13-5680329
022 C000007 2348000
022 D000007 0
022 A000008 CIBC
022 B000008 FOREIGN
022 C000008 2176640
022 D000008 0
022 A000009 ASSOCIATES CORP. OF NORTH AMERICA
022 B000009 52-1319768
022 C000009 2146518
022 D000009 0
022 A000010 NIKKO SECURITIES CO.
022 B000010 94-1302123
022 C000010 2102036
022 D000010 0
023 C000000 48176723
023 D000000 438750
027 000000 Y
077 A000000 Y
077 B000000 Y
080 A00AA00 VIGILANT INSURANCE COMPANY
080 B00AA00 NATIONAL UNION FIRE INSURANCE CO OF PITTS PA
080 C00AA00 125000
081 A00AA00 Y
081 B00AA00 171
082 A00AA00 N
082 B00AA00 0
083 A00AA00 N
083 B00AA00 0
<PAGE> PAGE 3
084 A00AA00 N
084 B00AA00 0
085 A00AA00 Y
085 B00AA00 N
025 A000101 BEAR, STEARNS & CO. INC.
025 B000101 13-3299429
025 C000101 D
025 D000101 19784
025 A000102 UBS SECURITIES INC.
025 B000102 13-2932996
025 C000102 D
025 D000102 14997
025 A000103 BARCLAYS DE ZOETE WEDD SECURITIES, INC.
025 B000103 13-3551367
025 C000103 D
025 D000103 10227
025 A000104 SBC CAPITAL MARKETS, INC.
025 B000104 13-3494485
025 C000104 D
025 D000104 35000
025 D000105 0
025 D000106 0
025 D000107 0
025 D000108 0
028 A010100 435850
028 A020100 187
028 A030100 0
028 A040100 469009
028 B010100 498901
028 B020100 236
028 B030100 0
028 B040100 403854
028 C010100 413845
028 C020100 254
028 C030100 0
028 C040100 395599
028 D010100 312024
028 D020100 417
028 D030100 0
028 D040100 317174
028 E010100 339868
028 E020100 485
028 E030100 0
028 E040100 256731
028 F010100 354541
028 F020100 460
028 F030100 0
028 F040100 472218
028 G010100 2355029
028 G020100 2039
028 G030100 0
<PAGE> PAGE 4
028 G040100 2314585
028 H000100 0
062 A000100 Y
062 B000100 0.0
062 C000100 0.0
062 D000100 8.5
062 E000100 0.0
062 F000100 3.8
062 G000100 0.0
062 H000100 0.0
062 I000100 67.0
062 J000100 3.8
062 K000100 0.0
062 L000100 13.5
062 M000100 0.0
062 N000100 0.0
062 O000100 0.0
062 P000100 0.0
062 Q000100 0.0
062 R000100 0.0
063 A000100 54
063 B000100 0.0
064 A000100 Y
064 B000100 N
071 A000100 0
071 B000100 0
071 C000100 0
071 D000100 0
072 A000100 12
072 B000100 29269
072 C000100 0
072 D000100 0
072 E000100 0
072 F000100 2598
072 G000100 0
072 H000100 0
072 I000100 158
072 J000100 76
072 K000100 0
072 L000100 4
072 M000100 60
072 N000100 26
072 O000100 1
072 P000100 0
072 Q000100 0
072 R000100 35
072 S000100 11
072 T000100 0
072 U000100 0
072 V000100 0
072 W000100 4
<PAGE> PAGE 5
072 X000100 2973
072 Y000100 0
072 Z000100 26296
072AA000100 11
072BB000100 6
072CC010100 0
072CC020100 0
072DD010100 26296
072DD020100 0
072EE000100 0
073 A010100 0.0506
073 A020100 0.0000
073 B000100 0.0000
073 C000100 0.0000
074 A000100 17161
074 B000100 45227
074 C000100 467996
074 D000100 0
074 E000100 0
074 F000100 0
074 G000100 0
074 H000100 0
074 I000100 0
074 J000100 0
074 K000100 0
074 L000100 1334
074 M000100 28
074 N000100 531746
074 O000100 0
074 P000100 243
074 Q000100 0
074 R010100 0
074 R020100 0
074 R030100 0
074 R040100 67
074 S000100 0
074 T000100 531436
074 U010100 531443
074 U020100 0
074 V010100 1.00
074 V020100 0.00
074 W000100 0.9999
074 X000100 3887
074 Y000100 0
075 A000100 519522
075 B000100 0
076 000100 0.00
025 A000201 BARCLAYS DE ZOETE WEDD SECURITIES, INC.
025 B000201 13-3551367
025 C000201 D
025 D000201 6803
<PAGE> PAGE 6
025 A000202 CIBC
025 B000202 FOREIGN
025 C000202 D
025 D000202 12000
025 A000203 SBC CAPITAL MARKETS, INC.
025 B000203 13-3498485
025 C000203 D
025 D000203 5000
025 A000204 UBS SECURITIES INC.
025 B000204 13-2932996
025 C000204 D
025 D000204 12000
025 D000205 0
025 D000206 0
025 D000207 0
025 D000208 0
028 A010200 110384
028 A020200 121
028 A030200 0
028 A040200 84791
028 B010200 44810
028 B020200 108
028 B030200 0
028 B040200 56519
028 C010200 87761
028 C020200 112
028 C030200 0
028 C040200 80456
028 D010200 92081
028 D020200 94
028 D030200 0
028 D040200 115653
028 E010200 58775
028 E020200 92
028 E030200 0
028 E040200 53575
028 F010200 64589
028 F020200 119
028 F030200 0
028 F040200 95984
028 G010200 458400
028 G020200 646
028 G030200 0
028 G040200 486978
028 H000200 0
062 A000200 Y
062 B000200 55.2
062 C000200 0.0
062 D000200 44.4
062 E000200 0.0
062 F000200 0.0
<PAGE> PAGE 7
062 G000200 0.0
062 H000200 0.0
062 I000200 0.0
062 J000200 0.0
062 K000200 0.0
062 L000200 0.0
062 M000200 0.0
062 N000200 0.0
062 O000200 0.0
062 P000200 0.0
062 Q000200 0.0
062 R000200 0.0
063 A000200 85
063 B000200 0.0
064 A000200 Y
064 B000200 N
071 A000200 0
071 B000200 0
071 C000200 0
071 D000200 0
072 A000200 12
072 B000200 8229
072 C000200 0
072 D000200 0
072 E000200 0
072 F000200 754
072 G000200 0
072 H000200 0
072 I000200 32
072 J000200 69
072 K000200 0
072 L000200 4
072 M000200 17
072 N000200 31
072 O000200 1
072 P000200 0
072 Q000200 0
072 R000200 9
072 S000200 4
072 T000200 0
072 U000200 0
072 V000200 0
072 W000200 0
072 X000200 921
072 Y000200 0
072 Z000200 7308
072AA000200 64
072BB000200 3
072CC010200 0
072CC020200 0
072DD010200 7308
<PAGE> PAGE 8
072DD020200 0
072EE000200 0
073 A010200 0.0484
073 A020200 0.0000
073 B000200 0.0000
073 C000200 0.0000
074 A000200 82
074 B000200 47803
074 C000200 59471
074 D000200 0
074 E000200 0
074 F000200 0
074 G000200 0
074 H000200 0
074 I000200 0
074 J000200 0
074 K000200 0
074 L000200 381
074 M000200 32
074 N000200 107769
074 O000200 0
074 P000200 59
074 Q000200 0
074 R010200 0
074 R020200 0
074 R030200 0
074 R040200 16
074 S000200 0
074 T000200 107694
074 U010200 107694
074 U020200 0
074 V010200 1.00
074 V020200 0.00
074 W000200 1.0001
074 X000200 195
074 Y000200 0
075 A000200 150894
075 B000200 0
076 000200 0.00
SIGNATURE MICHAEL PETRUCELLI
TITLE ASSISTANT TREASURER
<TABLE> <S> <C>
<ARTICLE> 6
<CIK> 0000315783
<NAME> DREYFUS INSTITUTIONAL MONEY MARKET FUND
<SERIES>
<NUMBER> 001
<NAME> MONEY MARKET SERIES
<MULTIPLIER> 1000
<S> <C>
<PERIOD-TYPE> YEAR
<FISCAL-YEAR-END> DEC-31-1997
<PERIOD-END> DEC-31-1997
<INVESTMENTS-AT-COST> 513223
<INVESTMENTS-AT-VALUE> 513223
<RECEIVABLES> 1334
<ASSETS-OTHER> 17189
<OTHER-ITEMS-ASSETS> 0
<TOTAL-ASSETS> 531746
<PAYABLE-FOR-SECURITIES> 0
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 310
<TOTAL-LIABILITIES> 310
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 531436
<SHARES-COMMON-STOCK> 531443
<SHARES-COMMON-PRIOR> 483167
<ACCUMULATED-NII-CURRENT> 0
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> (7)
<OVERDISTRIBUTION-GAINS> 0
<ACCUM-APPREC-OR-DEPREC> 0
<NET-ASSETS> 531436
<DIVIDEND-INCOME> 0
<INTEREST-INCOME> 29269
<OTHER-INCOME> 0
<EXPENSES-NET> 2973
<NET-INVESTMENT-INCOME> 26296
<REALIZED-GAINS-CURRENT> 5
<APPREC-INCREASE-CURRENT> 0
<NET-CHANGE-FROM-OPS> 26301
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> (26296)
<DISTRIBUTIONS-OF-GAINS> 0
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 4633186
<NUMBER-OF-SHARES-REDEEMED> (4588425)
<SHARES-REINVESTED> 3515
<NET-CHANGE-IN-ASSETS> 48281
<ACCUMULATED-NII-PRIOR> 0
<ACCUMULATED-GAINS-PRIOR> (12)
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 2598
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 2973
<AVERAGE-NET-ASSETS> 519522
<PER-SHARE-NAV-BEGIN> 1.00
<PER-SHARE-NII> .051
<PER-SHARE-GAIN-APPREC> 0
<PER-SHARE-DIVIDEND> (.051)
<PER-SHARE-DISTRIBUTIONS> 0
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 1.00
<EXPENSE-RATIO> .006
<AVG-DEBT-OUTSTANDING> 0
<AVG-DEBT-PER-SHARE> 0
</TABLE>
<TABLE> <S> <C>
<ARTICLE> 6
<CIK> 0000315783
<NAME> DREYFUS INSTITUTIONAL MONEY MARKET FUND
<SERIES>
<NUMBER> 002
<NAME> GOVERNMENT SECURITIES SERIES
<MULTIPLIER> 1000
<S> <C>
<PERIOD-TYPE> YEAR
<FISCAL-YEAR-END> DEC-31-1997
<PERIOD-END> DEC-31-1997
<INVESTMENTS-AT-COST> 107274
<INVESTMENTS-AT-VALUE> 107274
<RECEIVABLES> 381
<ASSETS-OTHER> 114
<OTHER-ITEMS-ASSETS> 0
<TOTAL-ASSETS> 107769
<PAYABLE-FOR-SECURITIES> 0
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 75
<TOTAL-LIABILITIES> 75
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 107694
<SHARES-COMMON-STOCK> 107694
<SHARES-COMMON-PRIOR> 102786
<ACCUMULATED-NII-CURRENT> 0
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> 0
<OVERDISTRIBUTION-GAINS> 0
<ACCUM-APPREC-OR-DEPREC> 0
<NET-ASSETS> 107694
<DIVIDEND-INCOME> 0
<INTEREST-INCOME> 8229
<OTHER-INCOME> 0
<EXPENSES-NET> 921
<NET-INVESTMENT-INCOME> 7308
<REALIZED-GAINS-CURRENT> 61
<APPREC-INCREASE-CURRENT> 0
<NET-CHANGE-FROM-OPS> 7369
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> (7308)
<DISTRIBUTIONS-OF-GAINS> 0
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 954132
<NUMBER-OF-SHARES-REDEEMED> 950602
<SHARES-REINVESTED> 1379
<NET-CHANGE-IN-ASSETS> 4969
<ACCUMULATED-NII-PRIOR> 0
<ACCUMULATED-GAINS-PRIOR> 0
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 754
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 921
<AVERAGE-NET-ASSETS> 150894
<PER-SHARE-NAV-BEGIN> 1.00
<PER-SHARE-NII> .048
<PER-SHARE-GAIN-APPREC> 0
<PER-SHARE-DIVIDEND> (.048)
<PER-SHARE-DISTRIBUTIONS> 0
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 1.00
<EXPENSE-RATIO> .006
<AVG-DEBT-OUTSTANDING> 0
<AVG-DEBT-PER-SHARE> 0
</TABLE>
