Sarepta Therapeutics (SRPT) had the highest return in August 2012 by a mid-cap US stock, returning 72.1%.

ASSET	MONTH	% RETURN
Sarepta Therapeutics (SRPT)	August 2012	72.14%
Repligen (RGEN)	August 2012	40.84%
Visteon (VC)	August 2012	40.82%
Option Care Health (OPCH)	August 2012	32.4%
Nexstar Broadcasting (NXST)	August 2012	32.21%
DXC Technology (DXC)	August 2012	30.65%
Brookdale Senior Living (BKD)	August 2012	30.59%
Capri (CPRI)	August 2012	29.84%
SkyWest (SKYW)	August 2012	29.54%
Owens Corning (OC)	August 2012	28.36%
Louisiana-Pacific (LPX)	August 2012	28.18%
Uranium Energy (UEC)	August 2012	27.5%
VEON (VEON)	August 2012	26.55%
Grand Canyon Education (LOPE)	August 2012	26.16%
Universal Display (OLED)	August 2012	25.92%
Eagle Materials (EXP)	August 2012	25.74%
Fortuna Silver Mines (FSM)	August 2012	25.67%
MYR (MYRG)	August 2012	24.1%
New Oriental Education & Technology (EDU)	August 2012	23.3%
Eldorado Gold (EGO)	August 2012	23.27%
Archrock (AROC)	August 2012	23.01%
Axcelis Technologies (ACLS)	August 2012	22.95%
First Majestic Silver (AG)	August 2012	22.78%
InterDigital (IDCC)	August 2012	22.73%
Radian (RDN)	August 2012	22.72%

Mid-cap stocks are treated as having a market cap between $2B and $10B.