Frontline (FRO) had the highest return between 2003 and 2007 by a mid-cap US stock, returning 35,097.6%.

ASSET	YEARS	% RETURN
Frontline (FRO)	2003-2007	35,097.6%
Millicom International Cellular (TIGO)	2003-2007	6,042.47%
BRF SA ADR (BRFS)	2003-2007	5,577.81%
Companhia Energetica de Minas Gerais CEMIG Pref ADR (CIG)	2003-2007	5,465.85%
BlackBerry (BB)	2003-2007	5,066.29%
Gerdau SA ADR (GGB)	2003-2007	2,395.03%
Hub (HUBG)	2003-2007	2,105.71%
Cleveland-Cliffs (CLF)	2003-2007	1,966.26%
Bancolombia SA ADR (CIB)	2003-2007	1,704.72%
PLDT Inc ADR (PHI)	2003-2007	1,642.49%
Cal-Maine Foods (CALM)	2003-2007	1,441.4%
Allegheny Technologies (ATI)	2003-2007	1,427.08%
Middleby (MIDD)	2003-2007	1,381.52%
Stonex (SNEX)	2003-2007	1,366.81%
Icahn Enterprises (IEP)	2003-2007	1,327.94%
Range Resources (RRC)	2003-2007	1,319.56%
Carpenter Technology (CRS)	2003-2007	1,166.83%
Sterling Construction (STRL)	2003-2007	1,146.86%
Terex (TEX)	2003-2007	1,075.1%
Grupo Simec SAB de CV ADR (SIM)	2003-2007	1,049.99%
Turkcell Iletisim Hizmetleri AS (TKC)	2003-2007	1,019.14%
Braskem SA Class A (BAK)	2003-2007	990.84%
Amedisys (AMED)	2003-2007	985.26%
RadNet (RDNT)	2003-2007	979.79%
Diodes (DIOD)	2003-2007	955.94%

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