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GROUP ONE TRADING, L.P. Information

440 S. LASALLE STREET, CHICAGO, Illinois, 60605, (312) 431-2841

Report Date: 03/31/2013

Position Statistics:

Total Positions 1,742
New Positions 452
Increased Positions 914
Decreased Positions 808
Positions with Activity 1,722
Sold Out Positions 434
Total Mkt Value
(in $ millions)		 522

Sector Weighting

Basic Materials 6.07%
Capital Goods 1.96%
Conglomerates 0.68%
Consumer Cyclical 2.44%
Consumer/Non-Cyclical 5.04%
Energy 12.79%
Financial 13.01%
Healthcare 10.76%
Services 28.54%
Technology 16.06%
Transportation 1.26%
Utilities 0.95%

Institutional Holdings information is filed by major institutions on form 13-F with the Securities and Exchange Commission.

1,742 Positions as of 03/31/2013

Company Class Value of Shares ($1,000s) Change in Value ($1,000s) Change (%) Shares Held
21VIANET GROUP INC SPONSORED ADR -3 Sold Out 0
3-D SYS CORP DEL COM NEW 630 630 New 13,500
3M CO COM 212 67 46.15 1,900
3SBIO INC SPONSORED ADR 378 314 492.10 22,784
51JOB INC SP ADR REP COM 3 3 New 50
8X8 INC NEW COM 173 -114 (39.83) 23,314
AAR CORP COM 11 -111 (91.26) 546
AASTROM BIOSCIENCES INC COM NEW -3 (94.83) 266
ABBOTT LABS COM 7 New 200
ABBVIE INC COM -9 Sold Out 0
ABIOMED INC COM -48 Sold Out 0
ABRAXAS PETE CORP COM -87 Sold Out 0
ACACIA RESH CORP ACACIA TCH COM 669 14 2.18 28,335
ACADIA HEALTHCARE COMPANY INC COM 40 40 New 1,158
ACADIA PHARMACEUTICALS COM 3,504 1,880 115.80 264,028
ACCRETIVE HEALTH INC COM 280 242 631.35 25,312
ACCURAY INC COM 69 57 449.25 13,204
ACETO CORP COM -11 Sold Out 0
ACHILLION PHARMACEUTICALS INC COM 551 394 251.95 70,879
ACORDA THERAPEUTICS INC COM 10 10 New 300