Companhia Siderurgica Nacional ADR (SID) had the highest return between 1999 and 2003 by a mid-cap US stock, returning 1,755.5%.

ASSET	YEARS	% RETURN
Companhia Siderurgica Nacional ADR (SID)	1999-2003	1,755.47%
FTI Consulting (FCN)	1999-2003	1,487.42%
SSR Mining (SSRM)	1999-2003	1,222.64%
Perdoceo Education (PRDO)	1999-2003	960.08%
Meritage (MTH)	1999-2003	955.71%
Middleby (MIDD)	1999-2003	937.33%
Merit Medical Systems (MMSI)	1999-2003	851.28%
Hudbay Minerals (HBM)	1999-2003	825.08%
Light & Wonder (LNW)	1999-2003	805.07%
Cal-Maine Foods (CALM)	1999-2003	789.9%
Inter Parfums (IPAR)	1999-2003	743.02%
Diodes (DIOD)	1999-2003	734.18%
Gerdau SA ADR (GGB)	1999-2003	710.18%
Patterson-UTI Energy (PTEN)	1999-2003	698.3%
Primo Brands (PRMB)	1999-2003	672.69%
Innodata (INOD)	1999-2003	660.46%
Gildan Activewear (GIL)	1999-2003	626.56%
Penn National Gaming (PENN)	1999-2003	560.49%
Euronet Worldwide (EEFT)	1999-2003	555.96%
Prosperity Bancshares (PB)	1999-2003	524.99%
Comstock Resources (CRK)	1999-2003	505.49%
Brightstar Lottery (BRSL)	1999-2003	499.87%
BlackBerry (BB)	1999-2003	478.76%
Denison Mines (DNN)	1999-2003	471.36%
CarMax (KMX)	1999-2003	462.36%

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