Globalstar, Inc Common Stock (GSAT) had the highest return in September 2013 by a mid-cap US stock, returning 67.7%.

ASSET	MONTH	% RETURN
Globalstar, Inc Common Stock (GSAT)	September 2013	67.69%
Celldex Therapeutics (CLDX)	September 2013	60.39%
Catalyst Pharmaceuticals (CPRX)	September 2013	53.27%
Aehr Test Systems (AEHR)	September 2013	52.56%
Plug Power (PLUG)	September 2013	39.62%
Extreme Networks (EXTR)	September 2013	38.83%
Grupo Financiero Galicia SA ADR (GGAL)	September 2013	37.03%
Sarepta Therapeutics (SRPT)	September 2013	36.94%
Arrowhead Pharmaceuticals (ARWR)	September 2013	36.78%
Riot Blockchain (RIOT)	September 2013	35.66%
ACADIA Pharmaceuticals (ACAD)	September 2013	35.32%
Ambarella (AMBA)	September 2013	34.81%
BBVA Banco Frances SA ADR (BBAR)	September 2013	34.21%
Pampa Energia SA ADR (PAM)	September 2013	31.58%
Nexstar Broadcasting (NXST)	September 2013	30.9%
Vipshop (VIPS)	September 2013	28.83%
Simmons First National (SFNC)	September 2013	27.66%
Sibanye Gold Ltd ADR (SBSW)	September 2013	27.07%
Banco Macro SA B ADR (BMA)	September 2013	26.52%
Halozyme Therapeutics (HALO)	September 2013	24.04%
Chord Energy (CHRD)	September 2013	23.78%
Caesars Entertainment (CZR)	September 2013	23.3%
Hudbay Minerals (HBM)	September 2013	22.44%
Argan (AGX)	September 2013	22.4%
TAL Education (TAL)	September 2013	21.64%

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