Frontline (FRO) had the highest return between 2000 and 2005 by a mid-cap US stock, returning 9,678.7%.

ASSET	YEARS	% RETURN
Frontline (FRO)	2000-2005	9,678.71%
Amedisys (AMED)	2000-2005	2,972.15%
Companhia Energetica de Minas Gerais CEMIG Pref ADR (CIG)	2000-2005	2,347.27%
BRF SA ADR (BRFS)	2000-2005	2,338.81%
Meritage (MTH)	2000-2005	2,241.28%
Companhia Siderurgica Nacional ADR (SID)	2000-2005	1,940.78%
HF Sinclair (DINO)	2000-2005	1,907.46%
Middleby (MIDD)	2000-2005	1,504.53%
Penn National Gaming (PENN)	2000-2005	1,369.44%
Sterling Construction (STRL)	2000-2005	1,246.4%
FTI Consulting (FCN)	2000-2005	1,134.81%
CarMax (KMX)	2000-2005	1,130.22%
SSR Mining (SSRM)	2000-2005	1,127.19%
Range Resources (RRC)	2000-2005	1,100.51%
Comstock Resources (CRK)	2000-2005	938.64%
Gildan Activewear (GIL)	2000-2005	852.24%
Alliance Resource Partners (ARLP)	2000-2005	851.99%
Bank Ozk (OZK)	2000-2005	796.71%
St Joe (JOE)	2000-2005	783.82%
Boyd Gaming (BYD)	2000-2005	764.86%
Hudbay Minerals (HBM)	2000-2005	737.5%
Light & Wonder (LNW)	2000-2005	708.3%
CNX Resources (CNX)	2000-2005	696.94%
Methanex (MEOH)	2000-2005	693.11%
Seaboard (SEB)	2000-2005	687.83%

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