Semi-annual Report (management Company) (nsar-a)

000 A000000 12/31/2012 000 C000000 0000867969 000 D000000 N 000 E000000 NF 000 F000000 Y 000 G000000 N 000 H000000 N 000 I000000 6.1 000 J000000 A 001 A000000 MFS INSTITUTIONAL TRUST 001 B000000 811-6174 001 C000000 6179545000 002 A000000 111 Huntington Ave. 002 B000000 BOSTON 002 C000000 MA 002 D010000 02199 003 000000 N 004 000000 N 005 000000 N 006 000000 N 007 A000000 Y 007 B000000 2 007 C010700 7 007 C020700 MFS Institutional International Equity Fund 007 C030700 N 007 C011100 11 007 C021100 MFS Institutional Large Cap Value Fund 007 C031100 N 008 A00AA01 MASSACHUSETTS FINANCIAL SERVICES COMPANY 008 B00AA01 A 008 C00AA01 801-17352 008 D01AA01 BOSTON 008 D02AA01 MA 008 D03AA01 02199 010 A00AA01 MASSACHUSETTS FINANCIAL SERVICES 010 B00AA01 801-17352 010 C01AA01 BOSTON 010 C02AA01 MA 010 C03AA01 02199 011 A00AA01 MFS FUND DISTRIBUTORS, INC. 011 B00AA01 8-27864 011 C01AA01 BOSTON 011 C02AA01 MA 011 C03AA01 02199 012 A00AA01 MFS SERVICE CENTER, INC. 012 B00AA01 84-1316 012 C01AA01 BOSTON 012 C02AA01 MA 012 C03AA01 02199 013 A00AA01 DELOITTE & TOUCHE LLP 013 B01AA01 BOSTON

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013 B02AA01 MA 013 B03AA01 02116 015 A000701 THE BANK OF NEW YORK 015 B000701 S 015 C010701 NEW YORK 015 C020701 NY 015 C030701 10286 015 E010701 X 015 A000702 JPMORGAN CHASE BANK 015 B000702 C 015 C010702 NEW YORK 015 C020702 NY 015 C030702 10081 015 E010702 X 015 A000703 BANK OF AMERICA/MERRILL LYNCH 015 B000703 C 015 C010703 Charlotte 015 C020703 NC 015 C030703 28255 015 E010703 X 015 A001101 JPMORGAN CHASE BANK 015 B001101 C 015 C011101 NEW YORK 015 C021101 NY 015 C031101 10081 015 E011101 X 015 A001102 THE BANK OF NEW YORK 015 B001102 S 015 C011102 NEW YORK 015 C021102 NY 015 C031102 10286 015 E011102 X 015 A001103 BANK OF AMERICA/MERRILL LYNCH 015 B001103 C 015 C011103 Charlotte 015 C021103 NC 015 C031103 28255 018 00AA00 Y 019 A00AA00 N 019 B00AA00 0 020 A000001 CITIGROUP, INC. 020 B000001 13-3187336 020 C000001 246 020 A000002 MORGAN STANLEY 020 B000002 13-2655998 020 C000002 166 020 A000003 BANK OF AMERICA/MERRILL LYNCH 020 B000003 00-0000000 020 C000003 166 020 A000004 UBS AG 020 B000004 13-2638166

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020 C000004 128 020 A000005 CREDIT SUISSE GROUP 020 B000005 13-5659485 020 C000005 127 020 A000006 GOLDMAN SACHS GROUP, INC. 020 B000006 13-5108880 020 C000006 107 020 A000007 JPMORGAN CHASE & CO. 020 B000007 13-3224017 020 C000007 83 020 A000008 DEUTSCHE BANK AG 020 B000008 13-6124068 020 C000008 75 020 A000009 BARCLAYS PLC 020 C000009 32 020 A000010 MACQUARIE SECURITIES LTD. 020 B000010 00-0000000 020 C000010 32 021 000000 1263 022 A000001 UBS AG 022 B000001 13-2638166 022 C000001 10031 022 D000001 0 022 A000002 JPMORGAN CHASE & CO. 022 B000002 13-3224017 022 C000002 31 022 D000002 0 022 A000003 State Street Corp. 022 B000003 04-1867445 022 C000003 12 022 D000003 0 023 C000000 828821 023 D000000 813178 024 000700 Y 024 001100 Y 025 A000701 UBS AG 025 B000701 13-2638166 025 C000701 E 025 D000701 68111 025 A000702 BARCLAY'S INVESTMENTS, INC. 025 B000702 05-0346412 025 C000702 E 025 D000702 35649 025 A001101 JPMORGAN CHASE & CO. 025 B001101 13-3224017 025 C001101 E 025 D001101 5129 025 A001102 GOLDMAN SACHS GROUP, INC. 025 B001102 13-5108880 025 C001102 E 025 D001102 3755

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025 A001103 State Street Corp. 025 B001103 04-1867445 025 C001103 E 025 D001103 1473 025 A001104 WELLS FARGO & CO. 025 B001104 00-0000000 025 C001104 E 025 D001104 2932 026 A000000 N 026 B000000 Y 026 C000000 N 026 D000000 Y 026 E000000 N 026 F000000 N 026 G010000 N 026 G020000 N 026 H000000 N 027 000000 Y 028 A010700 190698 028 A020700 0 028 A030700 0 028 A040700 18526 028 B010700 60606 028 B020700 0 028 B030700 0 028 B040700 28962 028 C010700 171358 028 C020700 0 028 C030700 0 028 C040700 79516 028 D010700 198681 028 D020700 0 028 D030700 0 028 D040700 40459 028 E010700 128690 028 E020700 0 028 E030700 0 028 E040700 53880 028 F010700 200077 028 F020700 52025 028 F030700 0 028 F040700 129775 028 G010700 950110 028 G020700 52025 028 G030700 0 028 G040700 351118 028 H000700 0 028 A011100 951 028 A021100 0 028 A031100 0 028 A041100 804

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028 B011100 1309 028 B021100 0 028 B031100 0 028 B041100 1640 028 C011100 1180 028 C021100 0 028 C031100 0 028 C041100 3114 028 D011100 3100 028 D021100 0 028 D031100 0 028 D041100 2192 028 E011100 4157 028 E021100 0 028 E031100 0 028 E041100 3336 028 F011100 6034 028 F021100 3613 028 F031100 0 028 F041100 2321 028 G011100 16731 028 G021100 3613 028 G031100 0 028 G041100 13407 028 H001100 0 029 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 0 037 000700 N 037 001100 N 038 000700 0 038 001100 0 039 000700 N 039 001100 N 040 000700 N 040 001100 N 042 A000700 0 042 B000700 0 042 C000700 0 042 D000700 0 042 E000700 0 042 F000700 0 042 G000700 0

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042 H000700 0 042 A001100 0 042 B001100 0 042 C001100 0 042 D001100 0 042 E001100 0 042 F001100 0 042 G001100 0 042 H001100 0 043 000700 0 043 001100 0 044 000700 0 044 001100 0 045 000700 Y 045 001100 Y 046 000700 N 046 001100 N 047 000700 Y 047 001100 Y 048 000700 0.000 048 A010700 1000000 048 A020700 0.750 048 B010700 1500000 048 B020700 0.700 048 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 2500000 048 K020700 0.650 048 001100 0.550 048 A011100 0 048 A021100 0.000 048 B011100 0 048 B021100 0.000 048 C011100 0 048 C021100 0.000 048 D011100 0 048 D021100 0.000

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048 E011100 0 048 E021100 0.000 048 F011100 0 048 F021100 0.000 048 G011100 0 048 G021100 0.000 048 H011100 0 048 H021100 0.000 048 I011100 0 048 I021100 0.000 048 J011100 0 048 J021100 0.000 048 K011100 0 048 K021100 0.000 049 000700 N 049 001100 N 050 000700 N 050 001100 N 051 000700 N 051 001100 N 052 000700 N 052 001100 N 053 A000700 Y 053 B000700 Y 053 C000700 N 053 A001100 Y 053 B001100 Y 053 C001100 N 054 A00AA00 Y 054 B00AA00 N 054 C00AA00 N 054 D00AA00 N 054 E00AA00 N 054 F00AA00 N 054 G00AA00 N 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 A000700 N 055 B000700 N 055 A001100 N 055 B001100 N 056 000700 Y 056 001100 Y 057 000700 N 057 001100 N

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058 A000700 N 058 A001100 N 059 000700 Y 059 001100 Y 060 A000700 Y 060 B000700 Y 060 A001100 Y 060 B001100 Y 061 000700 3000000 061 001100 3000000 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 0.0 062 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 0.0 062 A001100 N 062 B001100 0.0 062 C001100 0.0 062 D001100 0.0 062 E001100 0.0 062 F001100 0.0 062 G001100 0.0 062 H001100 0.0 062 I001100 0.0 062 J001100 0.0 062 K001100 0.0 062 L001100 0.0 062 M001100 0.0 062 N001100 0.0 062 O001100 0.0 062 P001100 0.0 062 Q001100 0.0 062 R001100 0.0 063 A000700 0 063 B000700 0.0 063 A001100 0 063 B001100 0.0 066 A000700 Y

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066 B000700 N 066 C000700 Y 066 D000700 N 066 E000700 N 066 F000700 N 066 G000700 N 066 A001100 Y 066 B001100 N 066 C001100 Y 066 D001100 N 066 E001100 N 066 F001100 N 066 G001100 N 067 000700 N 067 001100 N 068 A000700 N 068 B000700 Y 068 A001100 N 068 B001100 N 069 000700 N 069 001100 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 N 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 Y 070 L010700 Y 070 L020700 Y 070 M010700 Y 070 M020700 Y 070 N010700 Y 070 N020700 Y 070 O010700 Y 070 O020700 N

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070 P010700 Y 070 P020700 Y 070 Q010700 N 070 Q020700 N 070 R010700 Y 070 R020700 N 070 A011100 Y 070 A021100 N 070 B011100 Y 070 B021100 N 070 C011100 Y 070 C021100 N 070 D011100 Y 070 D021100 N 070 E011100 Y 070 E021100 N 070 F011100 Y 070 F021100 N 070 G011100 Y 070 G021100 N 070 H011100 Y 070 H021100 N 070 I011100 Y 070 I021100 N 070 J011100 Y 070 J021100 N 070 K011100 Y 070 K021100 Y 070 L011100 Y 070 L021100 Y 070 M011100 Y 070 M021100 Y 070 N011100 Y 070 N021100 N 070 O011100 Y 070 O021100 N 070 P011100 Y 070 P021100 Y 070 Q011100 N 070 Q021100 N 070 R011100 Y 070 R021100 N 071 A000700 1002229 071 B000700 289977 071 C000700 3475017 071 D000700 7 071 A001100 17232 071 B001100 15090 071 C001100 140941 071 D001100 11 072 A000700 6

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072 B000700 342 072 C000700 33906 072 D000700 0 072 E000700 0 072 F000700 14047 072 G000700 269 072 H000700 0 072 I000700 161 072 J000700 379 072 K000700 0 072 L000700 33 072 M000700 28 072 N000700 80 072 O000700 0 072 P000700 0 072 Q000700 0 072 R000700 26 072 S000700 22 072 T000700 0 072 U000700 0 072 V000700 0 072 W000700 51 072 X000700 15096 072 Y000700 4 072 Z000700 19156 072AA000700 67385 072BB000700 384 072CC010700 502497 072CC020700 0 072DD010700 60000 072DD020700 0 072EE000700 0 072 A001100 6 072 B001100 0 072 C001100 2050 072 D001100 0 072 E001100 0 072 F001100 398 072 G001100 15 072 H001100 0 072 I001100 6 072 J001100 11 072 K001100 0 072 L001100 3 072 M001100 3 072 N001100 10 072 O001100 0 072 P001100 0 072 Q001100 0 072 R001100 23 072 S001100 1

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072 T001100 0 072 U001100 0 072 V001100 0 072 W001100 5 072 X001100 475 072 Y001100 5 072 Z001100 1580 072AA001100 1766 072BB001100 1148 072CC011100 8237 072CC021100 0 072DD011100 3014 072DD021100 0 072EE001100 2868 073 A010700 0.2500 073 A020700 0.0000 073 B000700 0.0000 073 C000700 0.0000 073 A011100 0.2100 073 A021100 0.0000 073 B001100 0.2000 073 C001100 0.0000 074 A000700 0 074 B000700 0 074 C000700 0 074 D000700 0 074 E000700 0 074 F000700 4590095 074 G000700 0 074 H000700 0 074 I000700 44980 074 J000700 7251 074 K000700 0 074 L000700 9901 074 M000700 119 074 N000700 4652346 074 O000700 4499 074 P000700 384 074 Q000700 0 074 R010700 0 074 R020700 0 074 R030700 0 074 R040700 11192 074 S000700 0 074 T000700 4636271 074 U010700 240901 074 U020700 0 074 V010700 19.25 074 V020700 0.00 074 W000700 0.0000 074 X000700 381

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074 Y000700 0 074 A001100 0 074 B001100 0 074 C001100 0 074 D001100 0 074 E001100 384 074 F001100 145626 074 G001100 0 074 H001100 0 074 I001100 2133 074 J001100 0 074 K001100 0 074 L001100 380 074 M001100 2 074 N001100 148525 074 O001100 20 074 P001100 9 074 Q001100 0 074 R011100 0 074 R021100 0 074 R031100 0 074 R041100 106 074 S001100 0 074 T001100 148390 074 U011100 15271 074 U021100 0 074 V011100 9.72 074 V021100 0.00 074 W001100 0.0000 074 X001100 15 074 Y001100 0 075 A000700 0 075 B000700 3993698 075 A001100 0 075 B001100 142878 076 000700 0.00 076 001100 0.00 077 A000000 N 078 000000 N 080 C00AA00 0 081 B00AA00 0 082 B00AA00 0 083 B00AA00 0 084 B00AA00 0 086 A010000 0 086 A020000 0 086 B010000 0 086 B020000 0 086 C010000 0 086 C020000 0 086 D010000 0

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086 D020000 0 086 E010000 0 086 E020000 0 086 F010000 0 086 F020000 0 SIGNATURE KINO CLARK TITLE ASSISTANT TREASURER