Applied Digital (APLD) had the highest return in April 2012 by a mid-cap US stock, returning 125%.

ASSET	MONTH	% RETURN
Applied Digital (APLD)	April 2012	125%
Vipshop (VIPS)	April 2012	24.14%
Universal Display (OLED)	April 2012	23.23%
Grifols SA ADR (GRFS)	April 2012	23.18%
Denison Mines (DNN)	April 2012	22.82%
Customers Bancorp (CUBI)	April 2012	20.1%
NewMarket (NEU)	April 2012	19.48%
Grupo Aeroportuario del Sureste SAB de CV ADR (ASR)	April 2012	19.16%
VNET Group Inc DRC (VNET)	April 2012	14.77%
Cirrus Logic (CRUS)	April 2012	14.51%
IES (IESC)	April 2012	14.51%
Hexcel (HXL)	April 2012	14.46%
Brinker International (EAT)	April 2012	14.44%
CVR Energy (CVI)	April 2012	14.01%
KAR Auction Services (KAR)	April 2012	13.93%
Melco Resorts & Entertainment (MLCO)	April 2012	13.7%
Aris Mining (ARMN)	April 2012	13.5%
PriceSmart (PSMT)	April 2012	13.15%
Alamo (ALG)	April 2012	12.9%
Central Garden & Pet (CENT)	April 2012	12.79%
Icahn Enterprises (IEP)	April 2012	12.64%
Comstock Resources (CRK)	April 2012	11.56%
Cavco Industries (CVCO)	April 2012	11.52%
Quaker Chemical (KWR)	April 2012	11.35%
Timken (TKR)	April 2012	11.28%

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