Aura Minerals Inc Common Shares (AUGO) had the highest return between 2016 and 2018 by a mid-cap US stock, returning 1,787.4%.

ASSET	YEARS	% RETURN
Aura Minerals Inc Common Shares (AUGO)	2016-2018	1,787.43%
Chemours (CC)	2016-2018	462.33%
Cleveland-Cliffs (CLF)	2016-2018	389.8%
Casella Waste Systems (CWST)	2016-2018	382.88%
Lantheus (LNTH)	2016-2018	374.24%
Novanta (NOVT)	2016-2018	370.5%
Skyline (SKY)	2016-2018	347.69%
Alpha Metallurgical Resources (AMR)	2016-2018	343.49%
Silvercorp Metals (SVM)	2016-2018	336.73%
Vicor (VICR)	2016-2018	318.96%
Appfolio (APPF)	2016-2018	307.85%
Wix (WIX)	2016-2018	306.39%
Ollie's Bargain Outlet Hldg (OLLI)	2016-2018	297.55%
Planet Fitness (PLNT)	2016-2018	290.95%
Freshpet (FRPT)	2016-2018	286.07%
Ingevity (NGVT)	2016-2018	280.41%
Compania de Minas Buenaventura SAA ADR (BVN)	2016-2018	279.55%
Talos Energy (TALO)	2016-2018	279.51%
Chart Industries (GTLS)	2016-2018	264.31%
Wingstop (WING)	2016-2018	262.56%
Ringcentral (RNG)	2016-2018	256.73%
TAL Education (TAL)	2016-2018	249.94%
NexGen Energy (NXE)	2016-2018	249.71%
Gerdau SA ADR (GGB)	2016-2018	235.48%
Match (MTCH)	2016-2018	234.61%

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