<PAGE> PAGE 1
000 B000000 12/31/93
000 C000000 862084
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 VANGUARD INSTITUTIONAL INDEX FUND
001 B000000 811-6093
001 C000000 6106691000
002 A000000 100 VANGUARD BOULEVARD
002 B000000 MALVERN
002 C000000 PA
002 D010000 19355
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 75
019 C000000 VANGUARDGR
020 A000001 MORGAN STANLEY & CO., INC.
020 B000001 13-2655998
020 C000001 167
020 A000002 PAINE WEBBER, INC.
020 B000002 13-2638166
020 C000002 64
020 A000003 CANTOR, FITZGERALD & CO.
020 B000003 95-1786286
020 C000003 20
020 A000004 W.H. NEWBOLD'S SON & CO.
020 B000004 23-1938859
020 C000004 15
020 A000005 NOMURA SECURITIES INTERNATIONAL, INC.
020 B000005 13-2642206
020 C000005 14
020 A000006 LEHMAN BROTHERS INC.
020 B000006 13-2518466
020 C000006 7
020 A000007 INSTINET CORPORATION
020 B000007 13-3443395
020 C000007 6
020 A000008 SCHWAB (CHARLES) & CO., INC.
020 B000008 94-1737782
020 C000008 1
020 A000009 FIRST BOSTON CORP.
<PAGE> PAGE 2
020 B000009 13-5659485
020 C000009 1
020 C000010 0
021 000000 295
022 A000001 SEI LIQUID ASSET TRUST PRIME OBLIGATION PORT.
022 B000001 04-6565149
022 C000001 432343
022 D000001 432343
022 A000002 MILES INC.
022 C000002 252613
022 D000002 0
022 A000003 CITY OF NEW YORK
022 C000003 230689
022 D000003 0
022 A000004 STATE OF MICHIGAN
022 C000004 196315
022 D000004 0
022 A000005 GOLDMAN SACHS & CO.
022 B000005 13-5108880
022 C000005 43968
022 D000005 0
022 A000006 500 PORTFOLIO/VANGUARD INDEX TRUST
022 B000006 23-1999755
022 C000006 13793
022 D000006 12157
022 A000007 LEHMAN BROTHERS INC.
022 B000007 13-2518466
022 C000007 24339
022 D000007 0
022 A000008 NOMURA SECURITIES INTERNATIONAL, INC.
022 B000008 13-2642206
022 C000008 22269
022 D000008 0
022 A000009 TROSTER SINGER
022 B000009 13-5515160
022 C000009 20718
022 D000009 843
022 A000010 MARINE MIDLAND BANK
022 C000010 0
022 D000010 18910
023 C000000 1434977
023 D000000 466685
028 A010000 74754
028 A020000 0
028 A030000 0
028 A040000 8898
028 B010000 58207
028 B020000 0
028 B030000 0
028 B040000 14992
028 C010000 99481
<PAGE> PAGE 3
028 C020000 11202
028 C030000 0
028 C040000 24603
028 D010000 103003
028 D020000 0
028 D030000 0
028 D040000 17813
028 E010000 103466
028 E020000 0
028 E030000 0
028 E040000 26790
028 F010000 398367
028 F020000 39835
028 F030000 0
028 F040000 54464
028 G010000 837278
028 G020000 51037
028 G030000 0
028 G040000 147560
028 H000000 0
062 A000000 N
062 B000000 0.0
062 C000000 0.0
062 D000000 0.0
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
062 L000000 0.0
062 M000000 0.0
062 N000000 0.0
062 O000000 0.0
062 P000000 0.0
062 Q000000 0.0
062 R000000 0.0
070 A010000 Y
070 A020000 N
070 B010000 Y
070 B020000 N
070 C010000 N
070 C020000 N
070 D010000 Y
070 D020000 N
070 E010000 N
070 E020000 N
070 F010000 Y
070 F020000 Y
070 G010000 Y
<PAGE> PAGE 4
070 G020000 N
070 H010000 Y
070 H020000 N
070 I010000 N
070 I020000 N
070 J010000 Y
070 J020000 Y
070 K010000 Y
070 K020000 Y
070 L010000 Y
070 L020000 Y
070 M010000 N
070 M020000 N
070 N010000 Y
070 N020000 Y
070 O010000 Y
070 O020000 N
070 P010000 N
070 P020000 N
070 Q010000 N
070 Q020000 N
070 R010000 N
070 R020000 N
071 A000000 1529027
071 B000000 83319
071 C000000 2162118
071 D000000 4
072 A000000 12
072 B000000 40
072 C000000 60480
072 D000000 0
072 E000000 0
072 F000000 0
072 G000000 1467
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 0
072 Q000000 0
072 R000000 0
072 S000000 0
072 T000000 0
072 U000000 0
072 V000000 0
072 W000000 0
072 X000000 1467
<PAGE> PAGE 5
072 Y000000 0
072 Z000000 59053
072AA000000 19447
072BB000000 1190
072CC010000 127110
072CC020000 0
072DD010000 67177
072DD020000 0
072EE000000 9977
073 A010000 1.1900
073 A020000 0.0000
073 B000000 0.1800
073 C000000 0.0000
074 A000000 0
074 B000000 0
074 C000000 5376
074 D000000 0
074 E000000 0
074 F000000 3106579
074 G000000 0
074 H000000 0
074 I000000 0
074 J000000 1179
074 K000000 0
074 L000000 52174
074 M000000 0
074 N000000 3165308
074 O000000 25109
074 P000000 166
074 Q000000 0
074 R010000 0
074 R020000 0
074 R030000 0
074 R040000 37097
074 S000000 0
074 T000000 3102936
074 U010000 70201
074 U020000 0
074 V010000 44.20
074 V020000 0.00
074 W000000 0.0000
074 X000000 135
074 Y000000 0
075 A000000 0
075 B000000 2169307
076 000000 0.00
077 A000000 Y
077 B000000 Y
077 C000000 N
077 D000000 N
077 E000000 N
<PAGE> PAGE 6
077 F000000 N
077 G000000 N
077 H000000 N
077 I000000 N
077 J000000 N
077 K000000 N
077 L000000 N
077 M000000 N
077 N000000 N
077 O000000 N
077 P000000 N
077 Q010000 N
077 Q020000 N
077 Q030000 N
078 000000 N
080 A000000 ICI MUTUAL INSURANCE COMPANY
080 C000000 110000
081 A000000 Y
081 B000000 91
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 GARY P. SOURA
TITLE ASST. VICE PRESIDENT