<PAGE> PAGE 1
000 A000000 11/30/98
000 C000000 0000939934
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 SEI INSTITUTIONAL INVESTMENTS TRUST
001 B000000 811-7257
001 C000000 6109896024
002 A000000 2 OLIVER STREET
002 B000000 BOSTON
002 C000000 MA
002 D010000 02109
003 000000 N
004 000000 N
005 000000 N
006 000000 N
007 A000000 Y
007 B000000 4
007 C010100 1
007 C020100 LARGE CAP FUND
007 C030100 N
007 C010200 2
007 C020200 SMALL CAP FUND
007 C030200 N
007 C010300 3
007 C020300 CORE FIXED INCOME FUND
007 C030300 N
007 C010400 4
007 C010500 5
007 C010600 6
007 C010700 7
007 C020700 INTERNATIONAL EQUITY FUND
007 C030700 N
007 C010800 8
007 C010900 9
007 C011000 10
010 A00AA01 SEI INVESTMENTS MUTUAL FUNDS SERVICES
010 C01AA01 WAYNE
010 C02AA01 PA
010 C03AA01 19087
010 C04AA01 0451
011 A00AA01 SEI INVESTMENTS DISTRIBUTION CO.
011 B00AA01 8-0000
011 C01AA01 WAYNE
011 C02AA01 PA
011 C03AA01 19087
011 C04AA01 0451
<PAGE> PAGE 2
012 A00AA01 SEI INVESTMENTS MUTUAL FUNDS SERVICES
012 B00AA01 84-0000
012 C01AA01 WAYNE
012 C02AA01 PA
012 C03AA01 19087
012 C04AA01 0451
013 A00AA01 PRICEWATERHOUSECOOPERS LLP
013 B01AA01 PHILADELPHIA
013 B02AA01 PA
013 B03AA01 19106
018 00AA00 Y
019 A00AA00 Y
019 B00AA00 52
019 C00AA00 SEIFINSVCO
020 A000001 BEAR STEARNS
020 B000001 13-2975144
020 C000001 119
020 A000002 MORGAN STANLEY
020 B000002 13-2655998
020 C000002 67
020 A000003 BROADCOURT
020 C000003 57
020 A000004 INSTINET
020 B000004 13-3443395
020 C000004 52
020 A000005 MERRILL LYNCH
020 B000005 13-5674085
020 C000005 61
020 A000006 SMITH BARNEY
020 B000006 13-2518466
020 C000006 46
020 A000007 PERSHING
020 C000007 41
020 A000008 SWISS BANK CORP
020 C000008 50
020 A000009 WARBURG
020 C000009 50
020 A000010 JP MORGAN
020 B000010 13-3224016
020 C000010 41
021 000000 584
022 A000001 MERRILL LYNCH
022 B000001 13-5674085
022 C000001 10520328
022 D000001 467214
022 A000002 JP MORGAN
022 B000002 13-3224016
022 C000002 4418660
022 D000002 571321
022 A000003 SALOMON BROTHERS
022 B000003 13-3082694
<PAGE> PAGE 3
022 C000003 264730
022 D000003 280536
022 A000004 DLJ
022 C000004 226610
022 D000004 183380
022 A000005 LEHMAN
022 B000005 13-2927667
022 C000005 245360
022 D000005 140395
022 A000006 FIRST BOSTON
022 B000006 13-5659485
022 C000006 194217
022 D000006 164390
022 A000007 GOLDMAN SACHS
022 B000007 13-5108880
022 C000007 85669
022 D000007 142994
022 A000008 SMITH BARNEY
022 B000008 13-2518466
022 C000008 134208
022 D000008 4972
022 A000009 BEAR STEARNS
022 B000009 13-2975144
022 C000009 54208
022 D000009 76159
022 A000010 LAWRENCE O'DONNELL
022 C000010 136384
022 D000010 150668
023 C000000 16280374
023 D000000 2182029
026 A000000 N
026 B000000 N
026 C000000 N
026 D000000 Y
026 E000000 N
026 F000000 N
026 G010000 N
026 G020000 N
026 H000000 N
027 000000 Y
029 00AA00 N
030 A00AA00 0
030 B00AA00 0.00
030 C00AA00 0.00
031 A00AA00 0
031 B00AA00 0
032 00AA00 0
033 00AA00 0
034 00AA00 N
035 00AA00 0
036 B00AA00 0
<PAGE> PAGE 4
037 00AA00 N
038 00AA00 0
039 00AA00 N
040 00AA00 N
041 00AA00 N
042 A00AA00 0
042 B00AA00 0
042 C00AA00 0
042 D00AA00 0
042 E00AA00 0
042 F00AA00 0
042 G00AA00 0
042 H00AA00 0
043 00AA00 0
044 00AA00 0
049 00AA00 N
050 00AA00 N
051 00AA00 N
052 00AA00 N
053 A00AA00 Y
053 B00AA00 Y
053 C00AA00 N
054 A00AA00 Y
054 B00AA00 Y
054 C00AA00 N
054 D00AA00 N
054 E00AA00 N
054 F00AA00 N
054 G00AA00 Y
054 H00AA00 Y
054 I00AA00 N
054 J00AA00 Y
054 K00AA00 N
054 L00AA00 N
054 M00AA00 Y
054 N00AA00 N
054 O00AA00 N
055 A00AA00 N
055 B00AA00 N
056 00AA00 Y
057 00AA00 N
058 A00AA00 N
059 00AA00 Y
060 A00AA00 Y
060 B00AA00 Y
061 00AA00 0
077 A000000 N
008 A000101 SEI INVESTMENTS MANAGEMENT CORPORATION
008 B000101 A
008 C000101 801-0000
008 D010101 OAKS
<PAGE> PAGE 5
008 D020101 PA
008 D030101 19456
008 D040101 1100
008 A000102 ALLIANCE CAPITAL MANAGEMENT
008 B000102 S
008 C000102 801-0000
008 D010102 NEW YORK
008 D020102 NY
008 D030102 10105
008 A000103 TCW FUNDS MANAGEMENT, INC.
008 B000103 S
008 C000103 801-0000
008 D010103 LOS ANGELES
008 D020103 CA
008 D030103 90017
008 A000104 LSV ASSET MANAGEMENT
008 B000104 S
008 C000104 801-0000
008 D010104 CHICAGO
008 D020104 IL
008 D030104 60602
008 A000105 MELLON EQUITY ASSOCIATES
008 B000105 S
008 C000105 801-0000
008 D010105 PITTSBURGH
008 D020105 PA
008 D030105 15258
008 A000106 SANFORD C. BERNSTEIN & CO.
008 B000106 S
008 C000106 801-0000
008 D010106 NEW YORK
008 D020106 NY
008 D030106 10153
008 A000107 PROVIDENT INVESTMENT COUNSEL
008 B000107 S
008 C000107 801-0000
008 D010107 PASADENA
008 D020107 CA
008 D030107 91101
015 A000101 FIRST UNION NATIONAL BANK
015 B000101 C
015 C010101 PHILADELPHIA
015 C020101 PA
015 C030101 19106
015 E010101 X
024 000100 Y
025 A000101 JP MORGAN
025 B000101 13-3224016
025 C000101 E
025 D000101 2202
025 A000102 JP MORGAN
<PAGE> PAGE 6
025 B000102 13-3224016
025 C000102 D
025 D000102 31505
025 A000103 BEAR STEARNS
025 B000103 13-2975144
025 C000103 E
025 D000103 2115
025 A000104 LEHMAN
025 B000104 13-2927667
025 C000104 E
025 D000104 2427
025 A000105 MORGAN STANLEY
025 B000105 13-2655998
025 C000105 E
025 D000105 7428
028 A010100 19492
028 A020100 3736
028 A030100 0
028 A040100 37825
028 B010100 26314
028 B020100 0
028 B030100 0
028 B040100 4169
028 C010100 49542
028 C020100 7689
028 C030100 0
028 C040100 72213
028 D010100 42718
028 D020100 3731
028 D030100 0
028 D040100 38250
028 E010100 28715
028 E020100 0
028 E030100 0
028 E040100 15237
028 F010100 51792
028 F020100 3819
028 F030100 0
028 F040100 4371
028 G010100 218572
028 G020100 18975
028 G030100 0
028 G040100 172065
028 H000100 0
045 000100 Y
046 000100 N
047 000100 Y
048 000100 0.400
048 A010100 0
048 A020100 0.000
048 B010100 0
<PAGE> PAGE 7
048 B020100 0.000
048 C010100 0
048 C020100 0.000
048 D010100 0
048 D020100 0.000
048 E010100 0
048 E020100 0.000
048 F010100 0
048 F020100 0.000
048 G010100 0
048 G020100 0.000
048 H010100 0
048 H020100 0.000
048 I010100 0
048 I020100 0.000
048 J010100 0
048 J020100 0.000
048 K010100 0
048 K020100 0.000
062 A000100 N
062 B000100 0.0
062 C000100 0.0
062 D000100 0.0
062 E000100 0.0
062 F000100 0.0
062 G000100 0.0
062 H000100 0.0
062 I000100 0.0
062 J000100 0.0
062 K000100 0.0
062 L000100 0.0
062 M000100 0.0
062 N000100 0.0
062 O000100 0.0
062 P000100 0.0
062 Q000100 0.0
062 R000100 0.0
066 A000100 Y
066 B000100 N
066 C000100 N
066 D000100 N
066 E000100 Y
066 F000100 N
066 G000100 N
067 000100 N
068 A000100 N
068 B000100 N
069 000100 N
070 A010100 Y
070 A020100 Y
070 B010100 Y
<PAGE> PAGE 8
070 B020100 N
070 C010100 Y
070 C020100 N
070 D010100 Y
070 D020100 N
070 E010100 Y
070 E020100 Y
070 F010100 Y
070 F020100 N
070 G010100 Y
070 G020100 N
070 H010100 Y
070 H020100 N
070 I010100 Y
070 I020100 N
070 J010100 Y
070 J020100 N
070 K010100 Y
070 K020100 Y
070 L010100 Y
070 L020100 N
070 M010100 N
070 M020100 N
070 N010100 Y
070 N020100 N
070 O010100 Y
070 O020100 N
070 P010100 Y
070 P020100 N
070 Q010100 N
070 Q020100 N
070 R010100 Y
070 R020100 N
071 A000100 595227
071 B000100 467567
071 C000100 1133711
071 D000100 41
072 A000100 6
072 B000100 1206
072 C000100 7909
072 D000100 0
072 E000100 0
072 F000100 2263
072 G000100 293
072 H000100 0
072 I000100 0
072 J000100 59
072 K000100 0
072 L000100 0
072 M000100 14
072 N000100 19
<PAGE> PAGE 9
072 O000100 0
072 P000100 0
072 Q000100 0
072 R000100 10
072 S000100 9
072 T000100 0
072 U000100 0
072 V000100 0
072 W000100 49
072 X000100 2716
072 Y000100 1179
072 Z000100 7578
072AA000100 0
072BB000100 7111
072CC010100 53640
072CC020100 0
072DD010100 7527
072DD020100 0
072EE000100 0
073 A010100 0.1100
073 A020100 0.0000
073 B000100 0.0000
073 C000100 0.0000
074 A000100 0
074 B000100 31505
074 C000100 8642
074 D000100 0
074 E000100 0
074 F000100 1310689
074 G000100 0
074 H000100 0
074 I000100 0
074 J000100 0
074 K000100 0
074 L000100 0
074 M000100 0
074 N000100 1350836
074 O000100 0
074 P000100 0
074 Q000100 0
074 R010100 0
074 R020100 0
074 R030100 0
074 R040100 711
074 S000100 0
074 T000100 1350125
074 U010100 80072262
074 U020100 0
074 V010100 16.86
074 V020100 0.00
074 W000100 0.0000
<PAGE> PAGE 10
074 X000100 14
074 Y000100 1958
075 A000100 0
075 B000100 1304072
076 000100 0.00
008 A000201 SEI INVESTMENTS MANAGEMENT CORPORATION
008 B000201 A
008 C000201 801-0000
008 D010201 OAKS
008 D020201 PA
008 D030201 19456
008 D040201 1100
008 A000202 NICHOLAS APPLEGATE CAPITAL MANAGEMENT
008 B000202 S
008 C000202 801-0000
008 D010202 SAN DIEGO
008 D020202 CA
008 D030202 92101
008 A000203 POLYNOUS CAPITAL MANAGEMENT
008 B000203 S
008 C000203 801-0000
008 D010203 SAN FRANCISCO
008 D020203 CA
008 D030203 94108
008 A000204 BOSTON PARTNERS ASSET MANAGEMENT
008 B000204 S
008 C000204 801-0000
008 D010204 BOSTON
008 D020204 MA
008 D030204 02111
008 A000205 SPYGLASS ASSET MANAGEMENT
008 B000205 S
008 C000205 801-0000
008 D010205 TOLEDO
008 D020205 OH
008 D030205 43606
008 A000206 FURMAN SELZ CAPITAL MANAGEMENT
008 B000206 S
008 C000206 801-0000
008 D010206 NEW YORK
008 D020206 NY
008 D030206 10169
008 A000207 LSV ASSET MANAGEMENT
008 B000207 S
008 C000207 801-0000
008 D010207 CHICAGO
008 D020207 IL
008 D030207 60602
008 A000208 ROBERTSON STEPHENS INVESTMENT MANAGEMENT
008 B000208 S
008 C000208 801-0000
<PAGE> PAGE 11
008 D010208 SAN FRANCISCO
008 D020208 CA
008 D030208 94104
015 A000201 FIRST UNION NATIONAL BANK
015 B000201 C
015 C010201 PHILADELPHIA
015 C020201 PA
015 C030201 19106
015 E010201 X
024 000200 Y
025 A000201 JP MORGAN
025 B000201 13-3224016
025 C000201 D
025 D000201 13028
025 D000202 0
025 D000203 0
025 D000204 0
025 D000205 0
025 D000206 0
025 D000207 0
025 D000208 0
028 A010200 22467
028 A020200 0
028 A030200 0
028 A040200 82214
028 B010200 37425
028 B020200 3666
028 B030200 0
028 B040200 8435
028 C010200 101138
028 C020200 0
028 C030200 0
028 C040200 23087
028 D010200 38920
028 D020200 0
028 D030200 0
028 D040200 15227
028 E010200 33054
028 E020200 3844
028 E030200 0
028 E040200 9325
028 F010200 61079
028 F020200 0
028 F030200 0
028 F040200 12741
028 G010200 294082
028 G020200 7510
028 G030200 0
028 G040200 151029
028 H000200 0
045 000200 Y
<PAGE> PAGE 12
046 000200 Y
047 000200 Y
048 000200 0.650
048 A010200 0
048 A020200 0.000
048 B010200 0
048 B020200 0.000
048 C010200 0
048 C020200 0.000
048 D010200 0
048 D020200 0.000
048 E010200 0
048 E020200 0.000
048 F010200 0
048 F020200 0.000
048 G010200 0
048 G020200 0.000
048 H010200 0
048 H020200 0.000
048 I010200 0
048 I020200 0.000
048 J010200 0
048 J020200 0.000
048 K010200 0
048 K020200 0.000
062 A000200 N
062 B000200 0.0
062 C000200 0.0
062 D000200 0.0
062 E000200 0.0
062 F000200 0.0
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
066 A000200 Y
066 B000200 N
066 C000200 Y
066 D000200 N
066 E000200 N
066 F000200 N
066 G000200 N
067 000200 N
<PAGE> PAGE 13
068 A000200 N
068 B000200 N
069 000200 N
070 A010200 Y
070 A020200 Y
070 B010200 Y
070 B020200 N
070 C010200 Y
070 C020200 N
070 D010200 Y
070 D020200 N
070 E010200 Y
070 E020200 N
070 F010200 Y
070 F020200 Y
070 G010200 Y
070 G020200 N
070 H010200 Y
070 H020200 N
070 I010200 Y
070 I020200 N
070 J010200 Y
070 J020200 N
070 K010200 Y
070 K020200 Y
070 L010200 Y
070 L020200 N
070 M010200 N
070 M020200 N
070 N010200 Y
070 N020200 N
070 O010200 Y
070 O020200 N
070 P010200 Y
070 P020200 N
070 Q010200 N
070 Q020200 N
070 R010200 Y
070 R020200 N
071 A000200 305904
071 B000200 222138
071 C000200 283422
071 D000200 78
072 A000200 6
072 B000200 918
072 C000200 526
072 D000200 0
072 E000200 0
072 F000200 991
072 G000200 76
072 H000200 0
<PAGE> PAGE 14
072 I000200 0
072 J000200 14
072 K000200 0
072 L000200 0
072 M000200 1
072 N000200 5
072 O000200 0
072 P000200 0
072 Q000200 0
072 R000200 2
072 S000200 2
072 T000200 0
072 U000200 0
072 V000200 0
072 W000200 18
072 X000200 1109
072 Y000200 289
072 Z000200 624
072AA000200 5694
072BB000200 0
072CC010200 11352
072CC020200 0
072DD010200 1288
072DD020200 0
072EE000200 8430
073 A010200 0.0300
073 A020200 0.0000
073 B000200 1.8500
073 C000200 0.0000
074 A000200 0
074 B000200 13028
074 C000200 3512
074 D000200 0
074 E000200 0
074 F000200 312787
074 G000200 0
074 H000200 0
074 I000200 0
074 J000200 0
074 K000200 0
074 L000200 0
074 M000200 0
074 N000200 329327
074 O000200 0
074 P000200 0
074 Q000200 0
074 R010200 0
074 R020200 0
074 R030200 0
074 R040200 141
074 S000200 0
<PAGE> PAGE 15
074 T000200 329186
074 U010200 29208630
074 U020200 0
074 V010200 11.27
074 V020200 0.00
074 W000200 0.0000
074 X000200 18
074 Y000200 685
075 A000200 0
075 B000200 316344
076 000200 0.00
008 A000301 SEI INVESTMENTS MANAGEMENT CORPORATION
008 B000301 A
008 C000301 801-0000
008 D010301 OAKS
008 D020301 PA
008 D030301 19456
008 D040301 1100
008 A000302 WESTERN ASSET MANAGEMENT
008 B000302 S
008 C000302 801-0000
008 D010302 PASADENA
008 D020302 CA
008 D030302 91105
008 A000303 FIRSTAR INVESTMENT RESEARCH & MANAGEMENT CO
008 B000303 S
008 C000303 801-0000
008 D010303 MILWAUKEE
008 D020303 WI
008 D030303 53202
008 A000304 BLACKROCK FINANCIAL MANAGEMENT, INC.
008 B000304 S
008 C000304 801-0000
008 D010304 NEW YORK
008 D020304 NY
008 D030304 10154
015 A000301 FIRST UNION NATIONAL BANK
015 B000301 C
015 C010301 PHILADELPHIA
015 C020301 PA
015 C030301 19106
015 E010301 X
025 A000301 JP MORGAN
025 B000301 13-3224016
025 C000301 D
025 D000301 138652
025 A000302 BEAR STEARNS
025 B000302 13-2975144
025 C000302 D
025 D000302 1465
025 A000303 GOLDMAN SACHS
<PAGE> PAGE 16
025 B000303 13-5108880
025 C000303 D
025 D000303 1684
025 A000304 LEHMAN
025 B000304 13-2927667
025 C000304 D
025 D000304 6819
025 A000305 MERRILL LYNCH
025 B000305 13-5674085
025 C000305 D
025 D000305 905
025 A000306 SALOMON BROTHERS
025 B000306 13-3082694
025 C000306 D
025 D000306 4820
028 A010300 7563
028 A020300 0
028 A030300 0
028 A040300 7983
028 B010300 57994
028 B020300 331
028 B030300 0
028 B040300 2080
028 C010300 27091
028 C020300 0
028 C030300 0
028 C040300 14533
028 D010300 8648
028 D020300 0
028 D030300 0
028 D040300 11367
028 E010300 5307
028 E020300 305
028 E030300 0
028 E040300 1641
028 F010300 9867
028 F020300 0
028 F030300 0
028 F040300 1885
028 G010300 116469
028 G020300 636
028 G030300 0
028 G040300 39490
028 H000300 0
045 000300 Y
046 000300 Y
047 000300 Y
048 000300 0.300
048 A010300 0
048 A020300 0.000
048 B010300 0
<PAGE> PAGE 17
048 B020300 0.000
048 C010300 0
048 C020300 0.000
048 D010300 0
048 D020300 0.000
048 E010300 0
048 E020300 0.000
048 F010300 0
048 F020300 0.000
048 G010300 0
048 G020300 0.000
048 H010300 0
048 H020300 0.000
048 I010300 0
048 I020300 0.000
048 J010300 0
048 J020300 0.000
048 K010300 0
048 K020300 0.000
062 A000300 Y
062 B000300 0.0
062 C000300 0.0
062 D000300 13.7
062 E000300 0.0
062 F000300 0.0
062 G000300 0.0
062 H000300 0.0
062 I000300 0.0
062 J000300 0.0
062 K000300 0.0
062 L000300 0.0
062 M000300 25.2
062 N000300 29.4
062 O000300 0.0
062 P000300 18.7
062 Q000300 13.0
062 R000300 0.0
063 A000300 0
063 B000300 14.5
064 A000300 N
064 B000300 N
066 A000300 N
067 000300 N
068 A000300 N
068 B000300 N
069 000300 N
070 A010300 Y
070 A020300 Y
070 B010300 Y
070 B020300 N
070 C010300 Y
<PAGE> PAGE 18
070 C020300 N
070 D010300 Y
070 D020300 N
070 E010300 Y
070 E020300 N
070 F010300 Y
070 F020300 N
070 G010300 Y
070 G020300 Y
070 H010300 Y
070 H020300 N
070 I010300 Y
070 I020300 N
070 J010300 Y
070 J020300 Y
070 K010300 Y
070 K020300 N
070 L010300 Y
070 L020300 N
070 M010300 N
070 M020300 N
070 N010300 Y
070 N020300 N
070 O010300 Y
070 O020300 N
070 P010300 Y
070 P020300 N
070 Q010300 N
070 Q020300 N
070 R010300 Y
070 R020300 N
071 A000300 1597509
071 B000300 1518135
071 C000300 782146
071 D000300 194
072 A000300 6
072 B000300 23625
072 C000300 0
072 D000300 0
072 E000300 0
072 F000300 1167
072 G000300 196
072 H000300 0
072 I000300 0
072 J000300 38
072 K000300 0
072 L000300 0
072 M000300 9
072 N000300 134
072 O000300 0
072 P000300 0
<PAGE> PAGE 19
072 Q000300 0
072 R000300 6
072 S000300 5
072 T000300 0
072 U000300 0
072 V000300 0
072 W000300 72
072 X000300 1627
072 Y000300 921
072 Z000300 22919
072AA000300 5694
072BB000300 0
072CC010300 11352
072CC020300 0
072DD010300 22911
072DD020300 0
072EE000300 0
073 A010300 0.3600
073 A020300 0.0000
073 B000300 0.2200
073 C000300 0.0000
074 A000300 0
074 B000300 137869
074 C000300 328
074 D000300 866824
074 E000300 0
074 F000300 0
074 G000300 0
074 H000300 572
074 I000300 0
074 J000300 61651
074 K000300 0
074 L000300 177448
074 M000300 0
074 N000300 1244692
074 O000300 222585
074 P000300 0
074 Q000300 0
074 R010300 0
074 R020300 0
074 R030300 0
074 R040300 176334
074 S000300 0
074 T000300 845773
074 U010300 78339419
074 U020300 0
074 V010300 10.80
074 V020300 0.00
074 W000300 0.0000
074 X000300 16
074 Y000300 1434
<PAGE> PAGE 20
075 A000300 0
075 B000300 816384
076 000300 0.00
008 A000701 ACADIAN ASSET MANAGEMENT
008 B000701 S
008 C000701 801-0000
008 D010701 BOSTON
008 D020701 MA
008 D030701 02110
008 A000702 SCOTTISH WIDOWS INVESTMENT
008 B000702 S
008 C000702 801-0000
008 D010702 EDINBURGH
008 D050702 SCOTLAND
008 D060702 EH38YF
008 A000703 SG PACIFIC
008 B000703 S
008 C000703 801-0000
008 D010703 NEW YORK
008 D020703 NY
008 D030703 10048
008 A000704 SEI INVESTMENTS MANAGEMENT
008 B000704 A
008 C000704 801-0000
008 D010704 OAKS
008 D020704 PA
008 D030704 19456
008 A000705 CAPITAL GUARDIAN TRUST COMPANY
008 B000705 S
008 C000705 801-0000
008 D010705 BREA
008 D020705 CA
008 D030705 92821
015 A000701 STATE STREET BANK AND TRUST
015 B000701 C
015 C010701 BOSTON
015 C020701 MA
015 C030701 02110
015 E040701 X
024 000700 N
028 A010700 22571
028 A020700 0
028 A030700 0
028 A040700 5845
028 B010700 12429
028 B020700 0
028 B030700 0
028 B040700 2597
028 C010700 28540
028 C020700 0
028 C030700 0
<PAGE> PAGE 21
028 C040700 26562
028 D010700 23606
028 D020700 0
028 D030700 0
028 D040700 15942
028 E010700 29421
028 E020700 0
028 E030700 0
028 E040700 10756
028 F010700 22880
028 F020700 0
028 F030700 0
028 F040700 18741
028 G010700 139447
028 G020700 0
028 G030700 0
028 G040700 80443
028 H000700 0
045 000700 Y
046 000700 N
047 000700 Y
048 000700 0.580
048 A010700 0
048 A020700 0.000
048 B010700 0
048 B020700 0.000
048 C010700 0
048 C020700 0.000
048 D010700 0
048 D020700 0.000
048 E010700 0
048 E020700 0.000
048 F010700 0
048 F020700 0.000
048 G010700 0
048 G020700 0.000
048 H010700 0
048 H020700 0.000
048 I010700 0
048 I020700 0.000
048 J010700 0
048 J020700 0.000
048 K010700 0
048 K020700 0.000
062 A000700 N
062 B000700 0.0
062 C000700 0.0
062 D000700 0.0
062 E000700 0.0
062 F000700 0.0
062 G000700 0.0
<PAGE> PAGE 22
062 H000700 0.0
062 I000700 0.0
062 J000700 0.0
062 K000700 0.0
062 L000700 0.0
062 M000700 0.0
062 N000700 0.0
062 O000700 0.0
062 P000700 0.0
062 Q000700 0.0
062 R000700 0.0
063 A000700 0
063 B000700 0.0
066 A000700 Y
066 B000700 N
066 C000700 Y
066 D000700 N
066 E000700 N
066 F000700 N
066 G000700 N
067 000700 N
068 A000700 N
068 B000700 Y
069 000700 N
070 A010700 Y
070 A020700 Y
070 B010700 Y
070 B020700 N
070 C010700 Y
070 C020700 N
070 D010700 Y
070 D020700 N
070 E010700 Y
070 E020700 N
070 F010700 Y
070 F020700 Y
070 G010700 Y
070 G020700 N
070 H010700 Y
070 H020700 N
070 I010700 Y
070 I020700 N
070 J010700 Y
070 J020700 N
070 K010700 Y
070 K020700 N
070 L010700 Y
070 L020700 Y
070 M010700 Y
070 M020700 Y
070 N010700 Y
<PAGE> PAGE 23
070 N020700 N
070 O010700 Y
070 O020700 N
070 P010700 Y
070 P020700 N
070 Q010700 Y
070 Q020700 N
070 R010700 Y
070 R020700 N
071 A000700 281009
071 B000700 224928
071 C000700 536620
071 D000700 42
072 A000700 6
072 B000700 601
072 C000700 4782
072 D000700 0
072 E000700 0
072 F000700 1421
072 G000700 139
072 H000700 0
072 I000700 0
072 J000700 160
072 K000700 0
072 L000700 8
072 M000700 18
072 N000700 11
072 O000700 0
072 P000700 0
072 Q000700 0
072 R000700 3
072 S000700 6
072 T000700 0
072 U000700 1
072 V000700 0
072 W000700 17
072 X000700 1784
072 Y000700 669
072 Z000700 4268
072AA000700 3621
072BB000700 0
072CC010700 0
072CC020700 11114
072DD010700 0
072DD020700 0
072EE000700 0
073 A010700 0.0000
073 A020700 0.0000
073 B000700 0.0000
073 C000700 0.0000
074 A000700 910
<PAGE> PAGE 24
074 B000700 13793
074 C000700 7228
074 D000700 0
074 E000700 0
074 F000700 582546
074 G000700 0
074 H000700 0
074 I000700 0
074 J000700 0
074 K000700 9705
074 L000700 2237
074 M000700 118
074 N000700 616537
074 O000700 945
074 P000700 0
074 Q000700 0
074 R010700 0
074 R020700 0
074 R030700 0
074 R040700 5393
074 S000700 0
074 T000700 610199
074 U010700 54243
074 U020700 0
074 V010700 11.25
074 V020700 0.00
074 W000700 0.0000
074 X000700 19
074 Y000700 0
075 A000700 0
075 B000700 555627
076 000700 0.00
SIGNATURE MARK NAGLE
TITLE CONTROLLER
<TABLE> <S> <C>
<ARTICLE> 6
<CIK> 0000939934
<NAME> SEI INSTITUTIONAL INVESTMENTS TRUST
<SERIES>
<NUMBER> 010
<NAME> LARGE CAP FUND
<MULTIPLIER> 1,000
<S> <C>
<PERIOD-TYPE> 6-MOS
<FISCAL-YEAR-END> MAY-31-1999
<PERIOD-START> JUN-01-1998
<PERIOD-END> NOV-30-1998
<INVESTMENTS-AT-COST> 1054339
<INVESTMENTS-AT-VALUE> 1350836
<RECEIVABLES> 0
<ASSETS-OTHER> 0
<OTHER-ITEMS-ASSETS> 0
<TOTAL-ASSETS> 1350836
<PAYABLE-FOR-SECURITIES> 0
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 711
<TOTAL-LIABILITIES> 711
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 1027553
<SHARES-COMMON-STOCK> 80072
<SHARES-COMMON-PRIOR> 70302
<ACCUMULATED-NII-CURRENT> 2317
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> 22209
<OVERDISTRIBUTION-GAINS> 0
<ACCUM-APPREC-OR-DEPREC> 298046
<NET-ASSETS> 1350125
<DIVIDEND-INCOME> 7909
<INTEREST-INCOME> 1206
<OTHER-INCOME> 0
<EXPENSES-NET> (1537)
<NET-INVESTMENT-INCOME> 7578
<REALIZED-GAINS-CURRENT> (3511)
<APPREC-INCREASE-CURRENT> 53640
<NET-CHANGE-FROM-OPS> 57707
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> (7527)
<DISTRIBUTIONS-OF-GAINS> 0
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 18661
<NUMBER-OF-SHARES-REDEEMED> (9377)
<SHARES-REINVESTED> 486
<NET-CHANGE-IN-ASSETS> 200788
<ACCUMULATED-NII-PRIOR> 2266
<ACCUMULATED-GAINS-PRIOR> 27241
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 3325
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 4175
<AVERAGE-NET-ASSETS> 1169177
<PER-SHARE-NAV-BEGIN> 16.35
<PER-SHARE-NII> .11
<PER-SHARE-GAIN-APPREC> .51
<PER-SHARE-DIVIDEND> (.11)
<PER-SHARE-DISTRIBUTIONS> 0
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 16.86
<EXPENSE-RATIO> .26
<AVG-DEBT-OUTSTANDING> 0
<AVG-DEBT-PER-SHARE> 0
</TABLE>
<TABLE> <S> <C>
<ARTICLE> 6
<CIK> 0000939934
<NAME> SEI INSTITUTIONAL INVESTMENTS TRUST
<SERIES>
<NUMBER> 020
<NAME> SMALL CAP FUND
<MULTIPLIER> 1,000
<S> <C>
<PERIOD-TYPE> 6-MOS
<FISCAL-YEAR-END> MAY-31-1999
<PERIOD-START> JUN-01-1998
<PERIOD-END> NOV-30-1998
<INVESTMENTS-AT-COST> 309505
<INVESTMENTS-AT-VALUE> 329327
<RECEIVABLES> 0
<ASSETS-OTHER> 0
<OTHER-ITEMS-ASSETS> 0
<TOTAL-ASSETS> 329327
<PAYABLE-FOR-SECURITIES> 0
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 141
<TOTAL-LIABILITIES> 141
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 331786
<SHARES-COMMON-STOCK> 29209
<SHARES-COMMON-PRIOR> 23051
<ACCUMULATED-NII-CURRENT> 190
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> (23195)
<OVERDISTRIBUTION-GAINS> 0
<ACCUM-APPREC-OR-DEPREC> 20405
<NET-ASSETS> 329186
<DIVIDEND-INCOME> 918
<INTEREST-INCOME> 526
<OTHER-INCOME> 0
<EXPENSES-NET> (820)
<NET-INVESTMENT-INCOME> 624
<REALIZED-GAINS-CURRENT> (46837)
<APPREC-INCREASE-CURRENT> (3908)
<NET-CHANGE-FROM-OPS> (50121)
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> (637)
<DISTRIBUTIONS-OF-GAINS> 0
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 9842
<NUMBER-OF-SHARES-REDEEMED> (3741)
<SHARES-REINVESTED> 57
<NET-CHANGE-IN-ASSETS> 26831
<ACCUMULATED-NII-PRIOR> 211
<ACCUMULATED-GAINS-PRIOR> 23634
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 1482
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 1718
<AVERAGE-NET-ASSETS> 304080
<PER-SHARE-NAV-BEGIN> 13.12
<PER-SHARE-NII> .03
<PER-SHARE-GAIN-APPREC> (1.85)
<PER-SHARE-DIVIDEND> (.03)
<PER-SHARE-DISTRIBUTIONS> 0
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 11.27
<EXPENSE-RATIO> .54
<AVG-DEBT-OUTSTANDING> 0
<AVG-DEBT-PER-SHARE> 0
</TABLE>
<TABLE> <S> <C>
<ARTICLE> 6
<CIK> 0000939934
<NAME> SEI INSTITUTIONAL INVESTMENTS TRUST
<SERIES>
<NUMBER> 030
<NAME> CORE FIXED INCOME
<MULTIPLIER> 1,000
<S> <C>
<PERIOD-TYPE> 6-MOS
<FISCAL-YEAR-END> MAY-31-1999
<PERIOD-START> JUN-01-1998
<PERIOD-END> NOV-30-1998
<INVESTMENTS-AT-COST> 980882
<INVESTMENTS-AT-VALUE> 1005593
<RECEIVABLES> 177448
<ASSETS-OTHER> 61651
<OTHER-ITEMS-ASSETS> 0
<TOTAL-ASSETS> 1244692
<PAYABLE-FOR-SECURITIES> 167756
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 231163
<TOTAL-LIABILITIES> 398919
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 808287
<SHARES-COMMON-STOCK> 78339
<SHARES-COMMON-PRIOR> 72221
<ACCUMULATED-NII-CURRENT> 2
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> 13076
<OVERDISTRIBUTION-GAINS> 0
<ACCUM-APPREC-OR-DEPREC> 24408
<NET-ASSETS> 845773
<DIVIDEND-INCOME> 0
<INTEREST-INCOME> 23625
<OTHER-INCOME> 0
<EXPENSES-NET> (706)
<NET-INVESTMENT-INCOME> 22919
<REALIZED-GAINS-CURRENT> 5694
<APPREC-INCREASE-CURRENT> 11352
<NET-CHANGE-FROM-OPS> 39965
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> (22911)
<DISTRIBUTIONS-OF-GAINS> 0
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 20410
<NUMBER-OF-SHARES-REDEEMED> (16064)
<SHARES-REINVESTED> 1772
<NET-CHANGE-IN-ASSETS> 82537
<ACCUMULATED-NII-PRIOR> 0
<ACCUMULATED-GAINS-PRIOR> 7381
<OVERDISTRIB-NII-PRIOR> (6)
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 1666
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 2264
<AVERAGE-NET-ASSETS> 783759
<PER-SHARE-NAV-BEGIN> 10.58
<PER-SHARE-NII> .36
<PER-SHARE-GAIN-APPREC> .22
<PER-SHARE-DIVIDEND> (.36)
<PER-SHARE-DISTRIBUTIONS> 0
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 10.80
<EXPENSE-RATIO> .18
<AVG-DEBT-OUTSTANDING> 0
<AVG-DEBT-PER-SHARE> 0
</TABLE>
<TABLE> <S> <C>
<ARTICLE> 6
<CIK> 0000939934
<NAME> SEI INSTITUTIONAL INVESTMENTS TRUST
<SERIES>
<NUMBER> 070
<NAME> INTERNATIONAL EQUITY
<MULTIPLIER> 1,000
<S> <C>
<PERIOD-TYPE> 6-MOS
<FISCAL-YEAR-END> MAY-31-1999
<PERIOD-START> JUN-01-1998
<PERIOD-END> NOV-30-1998
<INVESTMENTS-AT-COST> 566332
<INVESTMENTS-AT-VALUE> 603567
<RECEIVABLES> 11942
<ASSETS-OTHER> 1028
<OTHER-ITEMS-ASSETS> 0
<TOTAL-ASSETS> 616537
<PAYABLE-FOR-SECURITIES> 945
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 5393
<TOTAL-LIABILITIES> 6338
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 544969
<SHARES-COMMON-STOCK> 54243
<SHARES-COMMON-PRIOR> 48834
<ACCUMULATED-NII-CURRENT> 9391
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> 18054
<OVERDISTRIBUTION-GAINS> 0
<ACCUM-APPREC-OR-DEPREC> 37785
<NET-ASSETS> 610199
<DIVIDEND-INCOME> 4782
<INTEREST-INCOME> 601
<OTHER-INCOME> 0
<EXPENSES-NET> (1115)
<NET-INVESTMENT-INCOME> 4268
<REALIZED-GAINS-CURRENT> 3621
<APPREC-INCREASE-CURRENT> (11114)
<NET-CHANGE-FROM-OPS> (3225)
<EQUALIZATION> 59003
<DISTRIBUTIONS-OF-INCOME> 0
<DISTRIBUTIONS-OF-GAINS> 0
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 12941
<NUMBER-OF-SHARES-REDEEMED> (7531)
<SHARES-REINVESTED> 0
<NET-CHANGE-IN-ASSETS> 55778
<ACCUMULATED-NII-PRIOR> 6069
<ACCUMULATED-GAINS-PRIOR> 13487
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 1421
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 1784
<AVERAGE-NET-ASSETS> 555627
<PER-SHARE-NAV-BEGIN> 11.35
<PER-SHARE-NII> .05
<PER-SHARE-GAIN-APPREC> (.15)
<PER-SHARE-DIVIDEND> 0
<PER-SHARE-DISTRIBUTIONS> 0
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 11.25
<EXPENSE-RATIO> .40
<AVG-DEBT-OUTSTANDING> 0
<AVG-DEBT-PER-SHARE> 0
</TABLE>