Quantum Computing (QUBT) had the highest return in March 2015 by a mid-cap US stock, returning 200%.

ASSET	MONTH	% RETURN
Quantum Computing (QUBT)	March 2015	200%
Applied Digital (APLD)	March 2015	103.7%
Travere Therapeutics (TVTX)	March 2015	69.69%
Corcept Therapeutics (CORT)	March 2015	69.18%
Wayfair (W)	March 2015	41.06%
Ligand Pharmaceuticals (LGND)	March 2015	39.01%
Transportadora de Gas del Sur SA ADR (TGS)	March 2015	36.66%
Pampa Energia SA ADR (PAM)	March 2015	36.03%
Universal Display (OLED)	March 2015	35.15%
OneMain (OMF)	March 2015	34.47%
Supernus Pharmaceuticals (SUPN)	March 2015	34.33%
Ambarella (AMBA)	March 2015	29.97%
Globalstar, Inc Common Stock (GSAT)	March 2015	29.07%
Alamo (ALG)	March 2015	26.34%
Casella Waste Systems (CWST)	March 2015	25.57%
HealthEquity (HQY)	March 2015	24.95%
Installed Building Products (IBP)	March 2015	24.77%
Amicus Therapeutics (FOLD)	March 2015	24.2%
Globant (GLOB)	March 2015	23.81%
Centrus Energy (LEU)	March 2015	22.63%
BBVA Banco Frances SA ADR (BBAR)	March 2015	21.91%
Vipshop (VIPS)	March 2015	20.46%
Kadant (KAI)	March 2015	18.79%
Vail Resorts (MTN)	March 2015	18.69%
Ameresco (AMRC)	March 2015	18.4%

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