Supernus Pharmaceuticals (SUPN) had the highest return in June 2012 by a mid-cap US stock, returning 75%.

ASSET	MONTH	% RETURN
Supernus Pharmaceuticals (SUPN)	June 2012	74.95%
Aura Minerals Inc Common Shares (AUGO)	June 2012	70.71%
Centrus Energy (LEU)	June 2012	41.43%
Radian (RDN)	June 2012	40.01%
KB Home (KBH)	June 2012	39.8%
Ligand Pharmaceuticals (LGND)	June 2012	37.72%
Universal Display (OLED)	June 2012	32.33%
BioCryst Pharmaceuticals (BCRX)	June 2012	31.02%
ACADIA Pharmaceuticals (ACAD)	June 2012	30.37%
HCI (HCI)	June 2012	29.7%
Worthington Industries (WOR)	June 2012	29.53%
MakeMyTrip (MMYT)	June 2012	25.8%
Celldex Therapeutics (CLDX)	June 2012	25.42%
Builders FirstSource (BLDR)	June 2012	25.07%
Cavco Industries (CVCO)	June 2012	25.04%
Nektar Therapeutics (NKTR)	June 2012	23.21%
DaVita HealthCare Partners (DVA)	June 2012	22.72%
InterDigital (IDCC)	June 2012	21.79%
Neogen (NEOG)	June 2012	21.71%
Masimo (MASI)	June 2012	21.63%
Federal Signal (FSS)	June 2012	21.41%
Assured Guaranty (AGO)	June 2012	21.13%
MGIC Investment (MTG)	June 2012	21.01%
M/I Homes (MHO)	June 2012	20.36%
Central Garden & Pet Company A (CENTA)	June 2012	20.33%

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