Energy of Minas Gerais Co DRC (CIG.C) had the highest return in Q4 2018 by a mid-cap US stock, returning 144.9%.

ASSET	QUARTER	% RETURN
Energy of Minas Gerais Co DRC (CIG.C)	Q4 2018	144.93%
Companhia Energetica de Minas Gerais CEMIG Pref ADR (CIG)	Q4 2018	105.79%
American Superconductor (AMSC)	Q4 2018	59.29%
Companhia Paranaense de Energia Pref ADR (ELP)	Q4 2018	52.01%
Ultrapar Participacoes SA ADR (UGP)	Q4 2018	45.28%
Stride (LRN)	Q4 2018	39.43%
SSR Mining (SSRM)	Q4 2018	38.8%
Guardant Health (GH)	Q4 2018	35.46%
Ondas (ONDS)	Q4 2018	33.33%
Veracyte (VCYT)	Q4 2018	30.91%
Virtu Financial (VIRT)	Q4 2018	27.89%
B2Gold (BTG)	Q4 2018	26.95%
Globalstar, Inc Common Stock (GSAT)	Q4 2018	25.93%
Sandstorm Gold Ltd N (SAND)	Q4 2018	23.59%
Compania de Minas Buenaventura SAA ADR (BVN)	Q4 2018	22.11%
Crocs (CROX)	Q4 2018	22.03%
Calix (CALX)	Q4 2018	20.37%
Zai Lab (ZLAB)	Q4 2018	19.51%
MarketAxess (MKTX)	Q4 2018	19.1%
Evertec (EVTC)	Q4 2018	18.62%
Turkcell Iletisim Hizmetleri AS (TKC)	Q4 2018	18.54%
Krystal Biotech (KRYS)	Q4 2018	17.47%
Dorman Products (DORM)	Q4 2018	16.91%
Aris Mining (ARMN)	Q4 2018	16.76%
HCI (HCI)	Q4 2018	16.71%

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