Sarepta Therapeutics (SRPT) had the best month between July 1, 2011 and December 31, 2012 by a large-cap US stock in July 2012, returning 146%.

ASSET	MONTH	% RETURN
Sarepta Therapeutics (SRPT)	July 2012	146%
Cheniere Energy (LNG)	October 2011	127.83%
Sarepta Therapeutics (SRPT)	August 2012	72.14%
Netflix (NFLX)	January 2012	71.03%
Illumina (ILMN)	January 2012	67.29%
XPO Logistics (XPO)	October 2011	65.7%
American Airlines (AAL)	January 2012	62.31%
Regeneron Pharmaceuticals (REGN)	January 2012	60.79%
Alnylam Pharmaceuticals (ALNY)	July 2012	60.57%
Seagate Technology (STX)	October 2011	58.02%
Vertex Pharmaceuticals (VRTX)	May 2012	56.35%
Genmab A-S (GMAB)	July 2012	55.96%
Insmed (INSM)	January 2012	54.49%
Align Technology (ALGN)	October 2011	53.53%
Sarepta Therapeutics (SRPT)	March 2012	49.51%
Skechers (SKX)	April 2012	47.59%
F5 Networks (FFIV)	October 2011	47.22%
XPO Logistics (XPO)	February 2012	45.83%
Netflix (NFLX)	October 2012	45.13%
EPAM Systems (EPAM)	March 2012	45.02%
T-Mobile US (TMUS)	July 2012	44.32%
CNH Industrial (CNH)	October 2011	44.05%
Cheniere Energy (LNG)	January 2012	43.87%
Nomura Holdings Inc ADR (NMR)	December 2012	43.44%
Juniper Networks (JNPR)	October 2011	43.02%

Large-cap stocks are treated as having a market cap of $10B+.