<PAGE> PAGE 1
000 B000000 07/31/98
000 C000000 0000783740
000 D000000 N
000 E000000 NF
000 F000000 Y
000 G000000 N
000 H000000 N
000 I000000 3.0.a
000 J000000 A
001 A000000 MFS SERIES TRUST X
001 B000000 811-4492
001 C000000 6179545000
002 A000000 500 BOYLSTON STREET
002 B000000 BOSTON
002 C000000 MA
002 D010000 02116
003 000000 N
004 000000 N
005 000000 N
006 000000 N
007 A000000 Y
007 B000000 4
007 C010100 1
007 C020100 MFS GOVERNMENT MORTGAGE FUND
007 C030100 N
007 C010200 2
007 C020200 MFS EMERGING MARKETS DEBT FUND
007 C030200 N
007 C010300 3
007 C020300 MFS SMALL CAP VALUE FUND
007 C030300 N
007 C010400 4
007 C020400 MFS STRATEGIC VALUE FUND
007 C030400 N
007 C010500 5
007 C010600 6
007 C010700 7
007 C010800 8
007 C010900 9
007 C011000 10
008 A00AA01 MASSACHUSETTS FINANCIAL SERVICES COMPANY
008 B00AA01 A
008 C00AA01 801-17352
008 D01AA01 BOSTON
008 D02AA01 MA
008 D03AA01 02116
010 A00AA01 MASSACHUSETTS FINANCIAL SERVICES COMPANY
010 B00AA01 701-17352
010 C01AA01 BOSTON
010 C02AA01 MA
010 C03AA01 02116
<PAGE> PAGE 2
011 A00AA01 MFS FUND DISTRIBUTORS, INC.
011 B00AA01 8-27864
011 C01AA01 BOSTON
011 C02AA01 MA
011 C03AA01 02116
012 A00AA01 MFS SERVICE CENTER, INC.
012 B00AA01 84-1316
012 C01AA01 BOSTON
012 C02AA01 MA
012 C03AA01 02116
015 A00AA01 STATE STREET BANK AND TRUST COMPANY
015 B00AA01 C
015 C01AA01 BOSTON
015 C02AA01 MA
015 C03AA01 02110
015 E01AA01 X
015 A00AA02 STATE STREET BANK AND TRUST COMPANY
015 B00AA02 S
015 C01AA02 BOSTON
015 C02AA02 MA
015 C03AA02 02110
015 E04AA02 X
015 A00AA03 THE BANK OF NEW YORK
015 B00AA03 S
015 C01AA03 NEW YORK
015 C02AA03 NY
015 C03AA03 10286
015 E01AA03 X
018 00AA00 Y
019 A00AA00 Y
019 B00AA00 52
019 C00AA00 MASSFINSER
020 A000001 INSTINET
020 C000001 0
020 A000002 NATIONAL FINANCIAL SERVIC
020 C000002 0
020 A000003 DUNLEVY + CO, INC.
020 C000003 0
020 A000004 BANQUES S.G. WARBURG
020 C000004 0
020 A000005 GOLDMAN SACHS + CO
020 C000005 0
020 A000006 SMITH BARNEY INC.
020 C000006 0
020 A000007 CS FIRST BOSTON CORP.
020 C000007 0
020 A000008 WEEDEN + CO.
020 C000008 0
020 A000009 ALEX,BROWN + SONS, INC.
020 C000009 0
020 A000010 MERRILL LYNCH PIERCE FENNER
<PAGE> PAGE 3
020 C000010 0
021 000000 2
022 A000001 GOLDMAN SACHS & CO.
022 B000001 13-5108880
022 C000001 7902874
022 D000001 33662
022 A000002 SALOMON BROTHERS
022 B000002 13-3082694
022 C000002 126325
022 D000002 150641
022 A000003 MERRILL LYNCH
022 B000003 13-5674085
022 C000003 118122
022 D000003 70239
022 A000004 MORGAN STANLEY
022 B000004 13-2655998
022 C000004 95059
022 D000004 48408
022 A000005 PAINE WEBBER
022 B000005 13-2638166
022 C000005 50815
022 D000005 62762
022 A000006 LEHMAN BROS.
022 B000006 13-2518466
022 C000006 54898
022 D000006 48869
022 A000007 CJ LAWRENCE
022 B000007 00-0000000
022 C000007 25534
022 D000007 34035
022 A000008 CS FIRST BOSTON CORP.
022 B000008 13-5659485
022 C000008 38880
022 D000008 17410
022 A000009 BEAR STEARNS
022 B000009 13-3299429
022 C000009 9441
022 D000009 46806
022 A000010 FIRST ALBANY CORP.
022 B000010 00-0000000
022 C000010 0
022 D000010 38270
023 C000000 8477682
023 D000000 615153
026 A000000 Y
026 B000000 Y
026 C000000 N
026 D000000 Y
026 E000000 N
026 F000000 N
026 G010000 N
<PAGE> PAGE 4
026 G020000 N
026 H000000 N
027 000000 Y
037 00AA00 N
038 00AA00 0
039 00AA00 N
040 00AA00 Y
041 00AA00 Y
054 A00AA00 Y
054 B00AA00 Y
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
077 A000000 Y
077 B000000 Y
077 H000000 Y
077 Q010000 Y
078 000000 N
080 A00AA00 NATIONAL UNION INSURANCE
080 B00AA00 FEDERAL INSURANCE
080 C00AA00 80000
081 A00AA00 Y
081 B00AA00 120
082 B00AA00 100
083 A00AA00 N
083 B00AA00 0
084 A00AA00 N
084 B00AA00 0
085 A00AA00 Y
085 B00AA00 N
086 A010000 0
086 A020000 0
086 B010000 0
086 B020000 0
086 C010000 0
086 C020000 0
086 D010000 0
086 D020000 0
086 E010000 0
086 E020000 0
086 F010000 0
<PAGE> PAGE 5
086 F020000 0
013 A000101 DELOITTE & TOUCHE LLP
013 B010101 BOSTON
013 B020101 MA
013 B030101 02110
024 000100 Y
025 A000101 GOLDMAN SACHS
025 B000101 13-5108880
025 C000101 D
025 D000101 1814
025 D000102 0
025 D000103 0
025 D000104 0
025 D000105 0
025 D000106 0
025 D000107 0
025 D000108 0
028 A010100 3692
028 A020100 2207
028 A030100 0
028 A040100 14658
028 B010100 3503
028 B020100 2223
028 B030100 0
028 B040100 17168
028 C010100 4437
028 C020100 2203
028 C030100 0
028 C040100 15905
028 D010100 6231
028 D020100 2168
028 D030100 0
028 D040100 16486
028 E010100 6717
028 E020100 2106
028 E030100 0
028 E040100 19325
028 F010100 8337
028 F020100 2102
028 F030100 0
028 F040100 22407
028 G010100 32917
028 G020100 13009
028 G030100 0
028 G040100 105949
028 H000100 27991
029 000100 Y
030 A000100 209
030 B000100 4.75
030 C000100 0.00
031 A000100 36
<PAGE> PAGE 6
031 B000100 0
032 000100 173
033 000100 0
034 000100 Y
035 000100 117
036 A000100 N
036 B000100 0
042 A000100 0
042 B000100 0
042 C000100 37
042 D000100 63
042 E000100 0
042 F000100 0
042 G000100 0
042 H000100 0
043 000100 4300
044 000100 0
045 000100 Y
046 000100 N
047 000100 Y
048 000100 0.450
048 A010100 0
048 A020100 0.000
048 B010100 0
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
049 000100 N
050 000100 N
051 000100 N
052 000100 N
053 A000100 Y
053 B000100 N
053 C000100 Y
055 A000100 Y
<PAGE> PAGE 7
055 B000100 N
056 000100 Y
057 000100 N
058 A000100 N
059 000100 Y
060 A000100 Y
060 B000100 Y
061 000100 1000
062 A000100 Y
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 6.3
062 N000100 92.7
062 O000100 0.0
062 P000100 0.0
062 Q000100 1.0
062 R000100 0.0
063 A000100 0
063 B000100 8.2
064 A000100 Y
064 B000100 N
066 A000100 N
067 000100 N
068 A000100 N
068 B000100 N
069 000100 N
070 A010100 Y
070 A020100 Y
070 B010100 N
070 B020100 N
070 C010100 Y
070 C020100 N
070 D010100 N
070 D020100 N
070 E010100 Y
070 E020100 Y
070 F010100 N
070 F020100 N
070 G010100 Y
070 G020100 N
070 H010100 N
070 H020100 N
<PAGE> PAGE 8
070 I010100 N
070 I020100 N
070 J010100 Y
070 J020100 N
070 K010100 Y
070 K020100 N
070 L010100 N
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 611206
071 B000100 743434
071 C000100 843522
071 D000100 72
072 A000100 12
072 B000100 64403
072 C000100 0
072 D000100 0
072 E000100 0
072 F000100 3930
072 G000100 123
072 H000100 0
072 I000100 1049
072 J000100 278
072 K000100 198
072 L000100 60
072 M000100 69
072 N000100 0
072 O000100 0
072 P000100 0
072 Q000100 0
072 R000100 40
072 S000100 6
072 T000100 3796
072 U000100 0
072 V000100 0
072 W000100 544
072 X000100 10093
072 Y000100 240
072 Z000100 54550
072AA000100 9772
<PAGE> PAGE 9
072BB000100 0
072CC010100 0
072CC020100 12706
072DD010100 40399
072DD020100 11610
072EE000100 2460
073 A010100 0.4100
073 A020100 0.3500
073 B000100 0.0200
073 C000100 0.0000
074 A000100 37
074 B000100 0
074 C000100 1814
074 D000100 804153
074 E000100 0
074 F000100 0
074 G000100 0
074 H000100 0
074 I000100 0
074 J000100 0
074 K000100 0
074 L000100 7710
074 M000100 7
074 N000100 813721
074 O000100 0
074 P000100 206
074 Q000100 0
074 R010100 0
074 R020100 0
074 R030100 0
074 R040100 1406
074 S000100 0
074 T000100 812109
074 U010100 98098
074 U020100 23191
074 V010100 6.69
074 V020100 6.70
074 W000100 0.0000
074 X000100 53835
074 Y000100 809
075 A000100 0
075 B000100 873284
076 000100 0.00
013 A000201 ERNST & YOUNG
013 B010201 BOSTON
013 B020201 MA
013 B030201 02116
024 000200 N
028 A010200 0
028 A020200 0
028 A030200 0
<PAGE> PAGE 10
028 A040200 0
028 B010200 1000
028 B020200 0
028 B030200 0
028 B040200 0
028 C010200 0
028 C020200 0
028 C030200 0
028 C040200 0
028 D010200 1
028 D020200 0
028 D030200 0
028 D040200 0
028 E010200 0
028 E020200 0
028 E030200 0
028 E040200 0
028 F010200 1
028 F020200 0
028 F030200 0
028 F040200 1
028 G010200 1002
028 G020200 0
028 G030200 0
028 G040200 1
028 H000200 1002
029 000200 N
030 A000200 0
030 B000200 0.00
030 C000200 0.00
031 A000200 0
031 B000200 0
032 000200 0
033 000200 0
034 000200 N
035 000200 0
036 B000200 0
042 A000200 0
042 B000200 0
042 C000200 0
042 D000200 0
042 E000200 0
042 F000200 0
042 G000200 0
042 H000200 0
043 000200 0
044 000200 0
045 000200 Y
046 000200 N
047 000200 Y
048 000200 0.850
<PAGE> PAGE 11
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
049 000200 N
050 000200 N
051 000200 N
052 000200 N
053 A000200 Y
053 B000200 Y
053 C000200 Y
055 A000200 Y
055 B000200 N
056 000200 Y
057 000200 N
058 A000200 N
059 000200 Y
060 A000200 N
060 B000200 N
061 000200 1000
062 A000200 Y
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
<PAGE> PAGE 12
062 N000200 12.0
062 O000200 0.0
062 P000200 0.0
062 Q000200 84.4
062 R000200 3.6
063 A000200 0
063 B000200 17.4
064 A000200 N
064 B000200 N
066 A000200 N
067 000200 N
068 A000200 N
068 B000200 Y
069 000200 N
070 A010200 Y
070 A020200 N
070 B010200 N
070 B020200 N
070 C010200 Y
070 C020200 N
070 D010200 N
070 D020200 N
070 E010200 Y
070 E020200 N
070 F010200 Y
070 F020200 N
070 G010200 Y
070 G020200 N
070 H010200 Y
070 H020200 N
070 I010200 N
070 I020200 N
070 J010200 Y
070 J020200 N
070 K010200 Y
070 K020200 N
070 L010200 Y
070 L020200 Y
070 M010200 Y
070 M020200 Y
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 1385
<PAGE> PAGE 13
071 B000200 506
071 C000200 742
071 D000200 68
072 A000200 5
072 B000200 31
072 C000200 0
072 D000200 0
072 E000200 0
072 F000200 3
072 G000200 0
072 H000200 0
072 I000200 0
072 J000200 1
072 K000200 0
072 L000200 8
072 M000200 0
072 N000200 4
072 O000200 0
072 P000200 0
072 Q000200 0
072 R000200 6
072 S000200 1
072 T000200 1
072 U000200 0
072 V000200 0
072 W000200 1
072 X000200 25
072 Y000200 19
072 Z000200 25
072AA000200 0
072BB000200 2
072CC010200 0
072CC020200 65
072DD010200 0
072DD020200 0
072EE000200 0
073 A010200 0.0000
073 A020200 0.0000
073 B000200 0.0000
073 C000200 0.0000
074 A000200 2
074 B000200 0
074 C000200 115
074 D000200 810
074 E000200 0
074 F000200 0
074 G000200 0
074 H000200 0
074 I000200 0
074 J000200 19
074 K000200 0
<PAGE> PAGE 14
074 L000200 14
074 M000200 0
074 N000200 960
074 O000200 0
074 P000200 0
074 Q000200 0
074 R010200 0
074 R020200 0
074 R030200 0
074 R040200 0
074 S000200 0
074 T000200 960
074 U010200 100
074 U020200 0
074 V010200 9.58
074 V020200 0.00
074 W000200 0.0000
074 X000200 6
074 Y000200 50000
075 A000200 0
075 B000200 986
076 000200 0.00
013 A000301 ERNST & YOUNG
013 B010301 BOSTON
013 B020301 MA
013 B030301 02116
024 000300 N
028 A010300 0
028 A020300 0
028 A030300 0
028 A040300 0
028 B010300 823
028 B020300 0
028 B030300 0
028 B040300 1
028 C010300 55
028 C020300 0
028 C030300 0
028 C040300 113
028 D010300 53
028 D020300 0
028 D030300 0
028 D040300 16
028 E010300 2
028 E020300 0
028 E030300 0
028 E040300 1
028 F010300 112
028 F020300 0
028 F030300 0
028 F040300 7
<PAGE> PAGE 15
028 G010300 1045
028 G020300 0
028 G030300 0
028 G040300 138
028 H000300 548
029 000300 N
030 A000300 0
030 B000300 0.00
030 C000300 0.00
031 A000300 0
031 B000300 0
032 000300 0
033 000300 0
034 000300 N
035 000300 0
036 B000300 0
042 A000300 0
042 B000300 0
042 C000300 0
042 D000300 0
042 E000300 0
042 F000300 0
042 G000300 0
042 H000300 0
043 000300 0
044 000300 0
045 000300 Y
046 000300 N
047 000300 Y
048 000300 0.900
048 A010300 0
048 A020300 0.000
048 B010300 0
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
<PAGE> PAGE 16
048 K020300 0.000
049 000300 N
050 000300 N
051 000300 N
052 000300 N
053 A000300 Y
053 B000300 Y
053 C000300 Y
055 A000300 N
055 B000300 N
056 000300 Y
057 000300 N
058 A000300 N
059 000300 Y
060 A000300 Y
060 B000300 Y
061 000300 1000
062 A000300 N
062 B000300 0.0
062 C000300 0.0
062 D000300 0.0
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 0.0
062 N000300 0.0
062 O000300 0.0
062 P000300 0.0
062 Q000300 0.0
062 R000300 0.0
063 A000300 0
063 B000300 0.0
066 A000300 Y
066 B000300 N
066 C000300 Y
066 D000300 N
066 E000300 N
066 F000300 N
066 G000300 N
067 000300 N
068 A000300 N
068 B000300 N
069 000300 N
070 A010300 Y
070 A020300 N
070 B010300 N
<PAGE> PAGE 17
070 B020300 N
070 C010300 Y
070 C020300 N
070 D010300 N
070 D020300 N
070 E010300 Y
070 E020300 N
070 F010300 Y
070 F020300 N
070 G010300 Y
070 G020300 N
070 H010300 Y
070 H020300 N
070 I010300 N
070 I020300 N
070 J010300 Y
070 J020300 N
070 K010300 Y
070 K020300 N
070 L010300 Y
070 L020300 Y
070 M010300 Y
070 M020300 Y
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 1254
071 B000300 503
071 C000300 754
071 D000300 67
072 A000300 5
072 B000300 2
072 C000300 2
072 D000300 0
072 E000300 0
072 F000300 3
072 G000300 0
072 H000300 0
072 I000300 0
072 J000300 1
072 K000300 0
072 L000300 11
072 M000300 0
072 N000300 4
<PAGE> PAGE 18
072 O000300 0
072 P000300 0
072 Q000300 0
072 R000300 5
072 S000300 1
072 T000300 1
072 U000300 0
072 V000300 0
072 W000300 0
072 X000300 26
072 Y000300 22
072 Z000300 0
072AA000300 55
072BB000300 0
072CC010300 0
072CC020300 57
072DD010300 0
072DD020300 0
072EE000300 0
073 A010300 0.0000
073 A020300 0.0000
073 B000300 0.0000
073 C000300 0.0000
074 A000300 0
074 B000300 0
074 C000300 65
074 D000300 0
074 E000300 0
074 F000300 748
074 G000300 0
074 H000300 0
074 I000300 0
074 J000300 11
074 K000300 0
074 L000300 95
074 M000300 0
074 N000300 919
074 O000300 15
074 P000300 0
074 Q000300 0
074 R010300 0
074 R020300 0
074 R030300 0
074 R040300 0
074 S000300 0
074 T000300 904
074 U010300 42
074 U020300 0
074 V010300 10.02
074 V020300 0.00
074 W000300 0.0000
<PAGE> PAGE 19
074 X000300 50
074 Y000300 0
075 A000300 0
075 B000300 810
076 000300 0.00
013 A000401 ERNST & YOUNG
013 B010401 BOSTON
013 B020401 MA
013 B030401 02116
024 000400 N
028 A010400 0
028 A020400 0
028 A030400 0
028 A040400 0
028 B010400 565
028 B020400 0
028 B030400 0
028 B040400 1
028 C010400 30
028 C020400 0
028 C030400 0
028 C040400 2
028 D010400 106
028 D020400 0
028 D030400 0
028 D040400 0
028 E010400 12
028 E020400 0
028 E030400 0
028 E040400 1
028 F010400 5
028 F020400 0
028 F030400 0
028 F040400 1
028 G010400 718
028 G020400 0
028 G030400 0
028 G040400 5
028 H000400 558
029 000400 N
030 A000400 0
030 B000400 0.00
030 C000400 0.00
031 A000400 0
031 B000400 0
032 000400 0
033 000400 0
034 000400 N
035 000400 0
036 B000400 0
042 A000400 0
<PAGE> PAGE 20
042 B000400 0
042 C000400 0
042 D000400 0
042 E000400 0
042 F000400 0
042 G000400 0
042 H000400 0
043 000400 0
044 000400 0
045 000400 Y
046 000400 N
047 000400 Y
048 000400 0.750
048 A010400 0
048 A020400 0.000
048 B010400 0
048 B020400 0.000
048 C010400 0
048 C020400 0.000
048 D010400 0
048 D020400 0.000
048 E010400 0
048 E020400 0.000
048 F010400 0
048 F020400 0.000
048 G010400 0
048 G020400 0.000
048 H010400 0
048 H020400 0.000
048 I010400 0
048 I020400 0.000
048 J010400 0
048 J020400 0.000
048 K010400 0
048 K020400 0.000
049 000400 N
050 000400 N
051 000400 N
052 000400 N
053 A000400 Y
053 B000400 Y
053 C000400 Y
055 A000400 N
055 B000400 N
056 000400 Y
057 000400 N
058 A000400 N
059 000400 Y
060 A000400 Y
060 B000400 Y
061 000400 1000
<PAGE> PAGE 21
062 A000400 N
062 B000400 0.0
062 C000400 0.0
062 D000400 0.0
062 E000400 0.0
062 F000400 0.0
062 G000400 0.0
062 H000400 0.0
062 I000400 0.0
062 J000400 0.0
062 K000400 0.0
062 L000400 0.0
062 M000400 0.0
062 N000400 0.0
062 O000400 0.0
062 P000400 0.0
062 Q000400 0.0
062 R000400 0.0
063 A000400 0
063 B000400 0.0
066 A000400 Y
066 B000400 N
066 C000400 Y
066 D000400 N
066 E000400 N
066 F000400 N
066 G000400 N
067 000400 N
068 A000400 N
068 B000400 N
069 000400 N
070 A010400 Y
070 A020400 N
070 B010400 N
070 B020400 N
070 C010400 Y
070 C020400 N
070 D010400 N
070 D020400 N
070 E010400 Y
070 E020400 N
070 F010400 Y
070 F020400 N
070 G010400 Y
070 G020400 N
070 H010400 Y
070 H020400 N
070 I010400 N
070 I020400 N
070 J010400 Y
070 J020400 N
<PAGE> PAGE 22
070 K010400 Y
070 K020400 N
070 L010400 Y
070 L020400 Y
070 M010400 Y
070 M020400 Y
070 N010400 Y
070 N020400 N
070 O010400 Y
070 O020400 N
070 P010400 Y
070 P020400 N
070 Q010400 N
070 Q020400 N
070 R010400 Y
070 R020400 N
071 A000400 1020
071 B000400 306
071 C000400 639
071 D000400 48
072 A000400 5
072 B000400 1
072 C000400 5
072 D000400 0
072 E000400 0
072 F000400 2
072 G000400 0
072 H000400 0
072 I000400 0
072 J000400 0
072 K000400 0
072 L000400 7
072 M000400 0
072 N000400 4
072 O000400 0
072 P000400 0
072 Q000400 0
072 R000400 5
072 S000400 1
072 T000400 1
072 U000400 0
072 V000400 0
072 W000400 1
072 X000400 21
072 Y000400 18
072 Z000400 3
072AA000400 36
072BB000400 0
072CC010400 0
072CC020400 0
072DD010400 0
<PAGE> PAGE 23
072DD020400 0
072EE000400 0
073 A010400 0.0000
073 A020400 0.0000
073 B000400 0.0000
073 C000400 0.0000
074 A000400 0
074 B000400 0
074 C000400 0
074 D000400 0
074 E000400 6
074 F000400 744
074 G000400 0
074 H000400 0
074 I000400 0
074 J000400 4
074 K000400 0
074 L000400 1
074 M000400 0
074 N000400 755
074 O000400 4
074 P000400 0
074 Q000400 0
074 R010400 0
074 R020400 0
074 R030400 0
074 R040400 0
074 S000400 0
074 T000400 751
074 U010400 55
074 U020400 0
074 V010400 10.66
074 V020400 0.00
074 W000400 0.0000
074 X000400 27
074 Y000400 0
075 A000400 0
075 B000400 679
076 000400 0.00
SIGNATURE JAMES O. YOST
TITLE ASSISTANT TREASURER
<TABLE> <S> <C>
<ARTICLE> 6
<CIK> 0000783740
<NAME> SERIES TRUST X
<SERIES>
<NUMBER> 021
<NAME> EMERGING MARKETS DEBT FUND CLASS A
<MULTIPLIER> 1
<S> <C>
<PERIOD-TYPE> 5-MOS
<FISCAL-YEAR-END> JUL-31-1998
<PERIOD-START> MAR-17-1998
<PERIOD-END> JUL-31-1998
<INVESTMENTS-AT-COST> 990633
<INVESTMENTS-AT-VALUE> 925167
<RECEIVABLES> 32930
<ASSETS-OTHER> 0
<OTHER-ITEMS-ASSETS> 1764
<TOTAL-ASSETS> 959861
<PAYABLE-FOR-SECURITIES> 0
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 116
<TOTAL-LIABILITIES> 116
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 1001461
<SHARES-COMMON-STOCK> 100021
<SHARES-COMMON-PRIOR> 0
<ACCUMULATED-NII-CURRENT> 26483
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> 0
<OVERDISTRIBUTION-GAINS> (3546)
<ACCUM-APPREC-OR-DEPREC> (64653)
<NET-ASSETS> 959745
<DIVIDEND-INCOME> 0
<INTEREST-INCOME> 30696
<OTHER-INCOME> 0
<EXPENSES-NET> (6090)
<NET-INVESTMENT-INCOME> 24606
<REALIZED-GAINS-CURRENT> (1669)
<APPREC-INCREASE-CURRENT> (64653)
<NET-CHANGE-FROM-OPS> (41716)
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> 0
<DISTRIBUTIONS-OF-GAINS> 0
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 100021
<NUMBER-OF-SHARES-REDEEMED> 0
<SHARES-REINVESTED> 0
<NET-CHANGE-IN-ASSETS> 959745
<ACCUMULATED-NII-PRIOR> 0
<ACCUMULATED-GAINS-PRIOR> 0
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 3144
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 25477
<AVERAGE-NET-ASSETS> 984,837
<PER-SHARE-NAV-BEGIN> 10.00
<PER-SHARE-NII> 0.25
<PER-SHARE-GAIN-APPREC> (0.67)
<PER-SHARE-DIVIDEND> 0
<PER-SHARE-DISTRIBUTIONS> 0
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 9.58
<EXPENSE-RATIO> 1.65
<AVG-DEBT-OUTSTANDING> 0
<AVG-DEBT-PER-SHARE> 0.00
</TABLE>
<TABLE> <S> <C>
<ARTICLE> 6
<CIK> 0000783740
<NAME> SERIES TRUST X
<SERIES>
<NUMBER> 022
<NAME> EMERGING MARKETS DEBT FUND CLASS I
<MULTIPLIER> 1
<S> <C>
<PERIOD-TYPE> 5-MOS
<FISCAL-YEAR-END> JUL-31-1998
<PERIOD-START> MAR-17-1998
<PERIOD-END> JUL-31-1998
<INVESTMENTS-AT-COST> 990633
<INVESTMENTS-AT-VALUE> 925167
<RECEIVABLES> 32930
<ASSETS-OTHER> 0
<OTHER-ITEMS-ASSETS> 1764
<TOTAL-ASSETS> 959861
<PAYABLE-FOR-SECURITIES> 0
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 116
<TOTAL-LIABILITIES> 116
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 1001461
<SHARES-COMMON-STOCK> 126
<SHARES-COMMON-PRIOR> 0
<ACCUMULATED-NII-CURRENT> 26483
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> 0
<OVERDISTRIBUTION-GAINS> (3546)
<ACCUM-APPREC-OR-DEPREC> (64653)
<NET-ASSETS> 959745
<DIVIDEND-INCOME> 0
<INTEREST-INCOME> 30696
<OTHER-INCOME> 0
<EXPENSES-NET> (6090)
<NET-INVESTMENT-INCOME> 24606
<REALIZED-GAINS-CURRENT> (1669)
<APPREC-INCREASE-CURRENT> (64653)
<NET-CHANGE-FROM-OPS> (41716)
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> 0
<DISTRIBUTIONS-OF-GAINS> 0
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 212
<NUMBER-OF-SHARES-REDEEMED> (86)
<SHARES-REINVESTED> 0
<NET-CHANGE-IN-ASSETS> 959745
<ACCUMULATED-NII-PRIOR> 0
<ACCUMULATED-GAINS-PRIOR> 0
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 3144
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 25477
<AVERAGE-NET-ASSETS> 1,155
<PER-SHARE-NAV-BEGIN> 10.00
<PER-SHARE-NII> 0.25
<PER-SHARE-GAIN-APPREC> (0.67)
<PER-SHARE-DIVIDEND> 0
<PER-SHARE-DISTRIBUTIONS> 0
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 9.58
<EXPENSE-RATIO> 1.65
<AVG-DEBT-OUTSTANDING> 0
<AVG-DEBT-PER-SHARE> 0.00
</TABLE>
<TABLE> <S> <C>
<ARTICLE> 6
<CIK> 0000783740
<NAME> MFS SERIES TRUST X
<SERIES>
<NUMBER> 011
<NAME> MFS GOVERNMENT MORTGAGE FUND CLASS A
<MULTIPLIER> 1
<S> <C>
<PERIOD-TYPE> YEAR
<FISCAL-YEAR-END> JUL-31-1998
<PERIOD-START> AUG-01-1997
<PERIOD-END> JUL-31-1998
<INVESTMENTS-AT-COST> 804658166
<INVESTMENTS-AT-VALUE> 805966765
<RECEIVABLES> 7710110
<ASSETS-OTHER> 7074
<OTHER-ITEMS-ASSETS> 37198
<TOTAL-ASSETS> 813721147
<PAYABLE-FOR-SECURITIES> 0
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 1611660
<TOTAL-LIABILITIES> 1611660
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 853171339
<SHARES-COMMON-STOCK> 98097509
<SHARES-COMMON-PRIOR> 97254938
<ACCUMULATED-NII-CURRENT> 0
<OVERDISTRIBUTION-NII> (184277)
<ACCUMULATED-NET-GAINS> 0
<OVERDISTRIBUTION-GAINS> (42192909)
<ACCUM-APPREC-OR-DEPREC> 1315334
<NET-ASSETS> 812109487
<DIVIDEND-INCOME> 0
<INTEREST-INCOME> 64403388
<OTHER-INCOME> 0
<EXPENSES-NET> 9853125
<NET-INVESTMENT-INCOME> 54550263
<REALIZED-GAINS-CURRENT> 9772406
<APPREC-INCREASE-CURRENT> (12706230)
<NET-CHANGE-FROM-OPS> 51616439
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> (40398677)
<DISTRIBUTIONS-OF-GAINS> (1910443)
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 18176669
<NUMBER-OF-SHARES-REDEEMED> (20335888)
<SHARES-REINVESTED> 3001790
<NET-CHANGE-IN-ASSETS> (127582573)
<ACCUMULATED-NII-PRIOR> 0
<ACCUMULATED-GAINS-PRIOR> 0
<OVERDISTRIB-NII-PRIOR> (164064)
<OVERDIST-NET-GAINS-PRIOR> (124937835)
<GROSS-ADVISORY-FEES> 3929806
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 10092700
<AVERAGE-NET-ASSETS> 873284304
<PER-SHARE-NAV-BEGIN> 6.72
<PER-SHARE-NII> 0.43
<PER-SHARE-GAIN-APPREC> (0.03)
<PER-SHARE-DIVIDEND> (0.41)
<PER-SHARE-DISTRIBUTIONS> (0.02)
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 6.69
<EXPENSE-RATIO> 0.97
<AVG-DEBT-OUTSTANDING> 0
<AVG-DEBT-PER-SHARE> 0
</TABLE>
<TABLE> <S> <C>
<ARTICLE> 6
<CIK> 0000783740
<NAME> MFS SERIES TRUST X
<SERIES>
<NUMBER> 012
<NAME> MFS GOVERNMENT MORTGAGE FUND CLASS B
<MULTIPLIER> 1
<S> <C>
<PERIOD-TYPE> YEAR
<FISCAL-YEAR-END> JUL-31-1998
<PERIOD-START> AUG-01-1997
<PERIOD-END> JUL-31-1998
<INVESTMENTS-AT-COST> 804658166
<INVESTMENTS-AT-VALUE> 805966765
<RECEIVABLES> 7710110
<ASSETS-OTHER> 7074
<OTHER-ITEMS-ASSETS> 37198
<TOTAL-ASSETS> 813721147
<PAYABLE-FOR-SECURITIES> 0
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 1611660
<TOTAL-LIABILITIES> 1611660
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 853171339
<SHARES-COMMON-STOCK> 23190632
<SHARES-COMMON-PRIOR> 42646140
<ACCUMULATED-NII-CURRENT> 0
<OVERDISTRIBUTION-NII> (184277)
<ACCUMULATED-NET-GAINS> 0
<OVERDISTRIBUTION-GAINS> (42192909)
<ACCUM-APPREC-OR-DEPREC> 1315334
<NET-ASSETS> 812109487
<DIVIDEND-INCOME> 0
<INTEREST-INCOME> 64403388
<OTHER-INCOME> 0
<EXPENSES-NET> 9853125
<NET-INVESTMENT-INCOME> 54550263
<REALIZED-GAINS-CURRENT> 9772406
<APPREC-INCREASE-CURRENT> (12706230)
<NET-CHANGE-FROM-OPS> 51616439
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> (11609634)
<DISTRIBUTIONS-OF-GAINS> (549017)
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 1436007
<NUMBER-OF-SHARES-REDEEMED> (21872935)
<SHARES-REINVESTED> 981420
<NET-CHANGE-IN-ASSETS> (127582573)
<ACCUMULATED-NII-PRIOR> 0
<ACCUMULATED-GAINS-PRIOR> 0
<OVERDISTRIB-NII-PRIOR> (164064)
<OVERDIST-NET-GAINS-PRIOR> (124937835)
<GROSS-ADVISORY-FEES> 3929806
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 10092700
<AVERAGE-NET-ASSETS> 873284304
<PER-SHARE-NAV-BEGIN> 6.72
<PER-SHARE-NII> 0.38
<PER-SHARE-GAIN-APPREC> (0.03)
<PER-SHARE-DIVIDEND> (0.35)
<PER-SHARE-DISTRIBUTIONS> (0.02)
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 6.70
<EXPENSE-RATIO> 1.72
<AVG-DEBT-OUTSTANDING> 0
<AVG-DEBT-PER-SHARE> 0
</TABLE>
<TABLE> <S> <C>
<ARTICLE> 6
<CIK> 0000783740
<NAME> MFS SERIES TRUST X
<SERIES>
<NUMBER> 013
<NAME> MFS GOVERNMENT MORTGAGE FUND CLASS I
<MULTIPLIER> 1
<S> <C>
<PERIOD-TYPE> YEAR
<FISCAL-YEAR-END> JUL-31-1998
<PERIOD-START> AUG-01-1997
<PERIOD-END> JUL-31-1998
<INVESTMENTS-AT-COST> 804658166
<INVESTMENTS-AT-VALUE> 805966765
<RECEIVABLES> 7710110
<ASSETS-OTHER> 7074
<OTHER-ITEMS-ASSETS> 37198
<TOTAL-ASSETS> 813721147
<PAYABLE-FOR-SECURITIES> 0
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 1611660
<TOTAL-LIABILITIES> 1611660
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 853171339
<SHARES-COMMON-STOCK> 7649
<SHARES-COMMON-PRIOR> 16882
<ACCUMULATED-NII-CURRENT> 0
<OVERDISTRIBUTION-NII> (184277)
<ACCUMULATED-NET-GAINS> 0
<OVERDISTRIBUTION-GAINS> (42192909)
<ACCUM-APPREC-OR-DEPREC> 1315334
<NET-ASSETS> 812109487
<DIVIDEND-INCOME> 0
<INTEREST-INCOME> 64403388
<OTHER-INCOME> 0
<EXPENSES-NET> 9853125
<NET-INVESTMENT-INCOME> 54550263
<REALIZED-GAINS-CURRENT> 9772406
<APPREC-INCREASE-CURRENT> (12706230)
<NET-CHANGE-FROM-OPS> 51616439
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> (5097)
<DISTRIBUTIONS-OF-GAINS> (241)
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 1275
<NUMBER-OF-SHARES-REDEEMED> (11278)
<SHARES-REINVESTED> 770
<NET-CHANGE-IN-ASSETS> (127582573)
<ACCUMULATED-NII-PRIOR> 0
<ACCUMULATED-GAINS-PRIOR> 0
<OVERDISTRIB-NII-PRIOR> (164064)
<OVERDIST-NET-GAINS-PRIOR> (124937835)
<GROSS-ADVISORY-FEES> 3929806
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 10092700
<AVERAGE-NET-ASSETS> 873284304
<PER-SHARE-NAV-BEGIN> 6.72
<PER-SHARE-NII> 0.44
<PER-SHARE-GAIN-APPREC> (0.02)
<PER-SHARE-DIVIDEND> (0.43)
<PER-SHARE-DISTRIBUTIONS> (0.02)
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 6.69
<EXPENSE-RATIO> 0.73
<AVG-DEBT-OUTSTANDING> 0
<AVG-DEBT-PER-SHARE> 0
</TABLE>
<TABLE> <S> <C>
<ARTICLE> 6
<CIK> 0000783740
<NAME> MFS SMALL CAP VALUE FUND-CLASS A
<SERIES>
<NUMBER> 031
<NAME> MFS SERIES TRUST X
<MULTIPLIER> 1
<S> <C>
<PERIOD-TYPE> YEAR
<FISCAL-YEAR-END> JUL-31-1998
<PERIOD-START> MAR-17-1998
<PERIOD-END> JUL-31-1998
<INVESTMENTS-AT-COST> 870590
<INVESTMENTS-AT-VALUE> 813154
<RECEIVABLES> 105429
<ASSETS-OTHER> 0
<OTHER-ITEMS-ASSETS> 727
<TOTAL-ASSETS> 919310
<PAYABLE-FOR-SECURITIES> 15217
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 30
<TOTAL-LIABILITIES> 15247
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 906230
<SHARES-COMMON-STOCK> 41760
<SHARES-COMMON-PRIOR> 0
<ACCUMULATED-NII-CURRENT> 277
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> 55038
<OVERDISTRIBUTION-GAINS> 0
<ACCUM-APPREC-OR-DEPREC> (57482)
<NET-ASSETS> 904063
<DIVIDEND-INCOME> 2324
<INTEREST-INCOME> 1981
<OTHER-INCOME> (56)
<EXPENSES-NET> (3895)
<NET-INVESTMENT-INCOME> 354
<REALIZED-GAINS-CURRENT> 54961
<APPREC-INCREASE-CURRENT> (57482)
<NET-CHANGE-FROM-OPS> (2167)
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> 0
<DISTRIBUTIONS-OF-GAINS> 0
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 54402
<NUMBER-OF-SHARES-REDEEMED> (12642)
<SHARES-REINVESTED> 0
<NET-CHANGE-IN-ASSETS> 904063
<ACCUMULATED-NII-PRIOR> 0
<ACCUMULATED-GAINS-PRIOR> 0
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 2696
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 25612
<AVERAGE-NET-ASSETS> 809961
<PER-SHARE-NAV-BEGIN> 10.00
<PER-SHARE-NII> 0.01
<PER-SHARE-GAIN-APPREC> 0.01
<PER-SHARE-DIVIDEND> 0
<PER-SHARE-DISTRIBUTIONS> 0
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 10.02
<EXPENSE-RATIO> 1.30
<AVG-DEBT-OUTSTANDING> 0
<AVG-DEBT-PER-SHARE> 0
</TABLE>
<TABLE> <S> <C>
<ARTICLE> 6
<CIK> 0000783740
<NAME> MFS SMALL CAP VALUE FUND-CLASS I
<SERIES>
<NUMBER> 032
<NAME> MFS SERIES TRUST X
<MULTIPLIER> 1
<S> <C>
<PERIOD-TYPE> YEAR
<FISCAL-YEAR-END> JUL-31-1998
<PERIOD-START> MAR-17-1998
<PERIOD-END> JUL-31-1998
<INVESTMENTS-AT-COST> 870590
<INVESTMENTS-AT-VALUE> 813154
<RECEIVABLES> 105429
<ASSETS-OTHER> 0
<OTHER-ITEMS-ASSETS> 727
<TOTAL-ASSETS> 919310
<PAYABLE-FOR-SECURITIES> 15217
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 30
<TOTAL-LIABILITIES> 15247
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 906230
<SHARES-COMMON-STOCK> 48489
<SHARES-COMMON-PRIOR> 0
<ACCUMULATED-NII-CURRENT> 277
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> 55038
<OVERDISTRIBUTION-GAINS> 0
<ACCUM-APPREC-OR-DEPREC> (57482)
<NET-ASSETS> 904063
<DIVIDEND-INCOME> 2324
<INTEREST-INCOME> 1981
<OTHER-INCOME> (56)
<EXPENSES-NET> (3895)
<NET-INVESTMENT-INCOME> 354
<REALIZED-GAINS-CURRENT> 54961
<APPREC-INCREASE-CURRENT> (57482)
<NET-CHANGE-FROM-OPS> (2167)
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> 0
<DISTRIBUTIONS-OF-GAINS> 0
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 49168
<NUMBER-OF-SHARES-REDEEMED> (679)
<SHARES-REINVESTED> 0
<NET-CHANGE-IN-ASSETS> 904063
<ACCUMULATED-NII-PRIOR> 0
<ACCUMULATED-GAINS-PRIOR> 0
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 2696
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 25612
<AVERAGE-NET-ASSETS> 809961
<PER-SHARE-NAV-BEGIN> 10.00
<PER-SHARE-NII> 0.01
<PER-SHARE-GAIN-APPREC> 0.01
<PER-SHARE-DIVIDEND> 0
<PER-SHARE-DISTRIBUTIONS> 0
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 10.02
<EXPENSE-RATIO> 1.30
<AVG-DEBT-OUTSTANDING> 0
<AVG-DEBT-PER-SHARE> 0
</TABLE>
<TABLE> <S> <C>
<ARTICLE> 6
<CIK> 0000783740
<NAME> MFS SERIES TRUST X
<SERIES>
<NUMBER> 041
<NAME> MFS STRATEGIC VALUE FUND A
<MULTIPLIER> 1
<S> <C>
<PERIOD-TYPE> 5-MOS
<FISCAL-YEAR-END> JUL-31-1998
<PERIOD-START> MAR-17-1998
<PERIOD-END> JUL-31-1998
<INVESTMENTS-AT-COST> 750052
<INVESTMENTS-AT-VALUE> 749856
<RECEIVABLES> 5349
<ASSETS-OTHER> 0
<OTHER-ITEMS-ASSETS> 109
<TOTAL-ASSETS> 755314
<PAYABLE-FOR-SECURITIES> 4400
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 26
<TOTAL-LIABILITIES> 4426
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 712446
<SHARES-COMMON-STOCK> 54888
<SHARES-COMMON-PRIOR> 0
<ACCUMULATED-NII-CURRENT> 3050
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> 35588
<OVERDISTRIBUTION-GAINS> 0
<ACCUM-APPREC-OR-DEPREC> (196)
<NET-ASSETS> 750888
<DIVIDEND-INCOME> 5257
<INTEREST-INCOME> 1067
<OTHER-INCOME> (132)
<EXPENSES-NET> (3139)
<NET-INVESTMENT-INCOME> 3053
<REALIZED-GAINS-CURRENT> 35585
<APPREC-INCREASE-CURRENT> (196)
<NET-CHANGE-FROM-OPS> 38442
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> 0
<DISTRIBUTIONS-OF-GAINS> 0
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 55362
<NUMBER-OF-SHARES-REDEEMED> (474)
<SHARES-REINVESTED> 0
<NET-CHANGE-IN-ASSETS> 750888
<ACCUMULATED-NII-PRIOR> 0
<ACCUMULATED-GAINS-PRIOR> 0
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 1885
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 21392
<AVERAGE-NET-ASSETS> 679070
<PER-SHARE-NAV-BEGIN> 10.00
<PER-SHARE-NII> .05
<PER-SHARE-GAIN-APPREC> .61
<PER-SHARE-DIVIDEND> 0
<PER-SHARE-DISTRIBUTIONS> 0
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 10.66
<EXPENSE-RATIO> 1.25
<AVG-DEBT-OUTSTANDING> 0
<AVG-DEBT-PER-SHARE> 0
</TABLE>
<TABLE> <S> <C>
<ARTICLE> 6
<CIK> 0000783740
<NAME> MFS SERIES TRUST X
<SERIES>
<NUMBER> 042
<NAME> MFS STRATEGIC VALUE FUND I
<MULTIPLIER> 1
<S> <C>
<PERIOD-TYPE> 5-MOS
<FISCAL-YEAR-END> JUL-31-1998
<PERIOD-START> MAR-17-1998
<PERIOD-END> JUL-31-1998
<INVESTMENTS-AT-COST> 750052
<INVESTMENTS-AT-VALUE> 749856
<RECEIVABLES> 5349
<ASSETS-OTHER> 0
<OTHER-ITEMS-ASSETS> 109
<TOTAL-ASSETS> 755314
<PAYABLE-FOR-SECURITIES> 4400
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 26
<TOTAL-LIABILITIES> 4426
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 712446
<SHARES-COMMON-STOCK> 15547
<SHARES-COMMON-PRIOR> 0
<ACCUMULATED-NII-CURRENT> 3050
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> 35588
<OVERDISTRIBUTION-GAINS> 0
<ACCUM-APPREC-OR-DEPREC> (196)
<NET-ASSETS> 750888
<DIVIDEND-INCOME> 5257
<INTEREST-INCOME> 1067
<OTHER-INCOME> (132)
<EXPENSES-NET> (3139)
<NET-INVESTMENT-INCOME> 3053
<REALIZED-GAINS-CURRENT> 35585
<APPREC-INCREASE-CURRENT> (196)
<NET-CHANGE-FROM-OPS> 38442
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> 0
<DISTRIBUTIONS-OF-GAINS> 0
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 15558
<NUMBER-OF-SHARES-REDEEMED> (11)
<SHARES-REINVESTED> 0
<NET-CHANGE-IN-ASSETS> 750888
<ACCUMULATED-NII-PRIOR> 0
<ACCUMULATED-GAINS-PRIOR> 0
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 1885
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 21392
<AVERAGE-NET-ASSETS> 679070
<PER-SHARE-NAV-BEGIN> 10.00
<PER-SHARE-NII> .05
<PER-SHARE-GAIN-APPREC> .60
<PER-SHARE-DIVIDEND> 0
<PER-SHARE-DISTRIBUTIONS> 0
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 10.65
<EXPENSE-RATIO> 1.25
<AVG-DEBT-OUTSTANDING> 0
<AVG-DEBT-PER-SHARE> 0
</TABLE>