RadNet (RDNT) had the highest return between 2000 and 2001 by a mid-cap US stock, returning 1,523.5%.

ASSET	YEARS	% RETURN
RadNet (RDNT)	2000-2001	1,523.53%
CarMax (KMX)	2000-2001	910.67%
Option Care Health (OPCH)	2000-2001	630.26%
FTI Consulting (FCN)	2000-2001	556.01%
Caesars Entertainment (CZR)	2000-2001	401.96%
Itron (ITRI)	2000-2001	399.79%
Meritage (MTH)	2000-2001	377.2%
Manhattan Associates (MANH)	2000-2001	277.65%
DaVita HealthCare Partners (DVA)	2000-2001	262.22%
Perdoceo Education (PRDO)	2000-2001	260.84%
OSI Systems (OSIS)	2000-2001	250.56%
Brightstar Lottery (BRSL)	2000-2001	235.21%
M/I Homes (MHO)	2000-2001	225.15%
Merit Medical Systems (MMSI)	2000-2001	211.33%
Cabot (CBT)	2000-2001	210.02%
Primo Brands (PRMB)	2000-2001	202.86%
ICU Medical (ICUI)	2000-2001	194.22%
ESCO Technologies (ESE)	2000-2001	193.53%
White Mountains Insurance (WTM)	2000-2001	192.95%
Penske Automotive (PAG)	2000-2001	192.88%
Encompass Health (EHC)	2000-2001	178.96%
Balchem (BCPC)	2000-2001	173.34%
Powell Industries (POWL)	2000-2001	173.02%
CNX Resources (CNX)	2000-2001	172.85%
Bio-Rad Laboratories (BIO)	2000-2001	170.8%

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