Weatherford International (WFRD) had the highest return in Q4 2019 by a mid-cap US stock, returning 99,981%.

ASSET	QUARTER	% RETURN
Weatherford International (WFRD)	Q4 2019	99,981.02%
Axsome Therapeutics (AXSM)	Q4 2019	410.42%
Immunitybio (IBRX)	Q4 2019	208.13%
Mirum Pharmaceuticals (MIRM)	Q4 2019	145.45%
Arrowhead Pharmaceuticals (ARWR)	Q4 2019	125.73%
Surgery Partners (SGRY)	Q4 2019	112.13%
BW LPG (BWLP)	Q4 2019	102.13%
TG Therapeutics (TGTX)	Q4 2019	96.81%
Sitime (SITM)	Q4 2019	96.15%
Soleno Therapeutics (SLNO)	Q4 2019	96%
Cidara Therapeutics (CDTX)	Q4 2019	93.94%
Hecla Mining (HL)	Q4 2019	90.65%
Centrus Energy (LEU)	Q4 2019	86.45%
Uniqure (QURE)	Q4 2019	83.74%
Sibanye Gold Ltd ADR (SBSW)	Q4 2019	81.2%
Sarepta Therapeutics (SRPT)	Q4 2019	71.6%
Amneal Pharmaceuticals, Inc Class A Common Stock (AMRX)	Q4 2019	65.07%
Synaptics (SYNA)	Q4 2019	64.38%
Crinetics Pharmaceuticals (CRNX)	Q4 2019	63.13%
Krystal Biotech (KRYS)	Q4 2019	61.08%
Immunovant (IMVT)	Q4 2019	58.38%
Gerdau SA ADR (GGB)	Q4 2019	57.49%
Vicor (VICR)	Q4 2019	57.09%
Qorvo (QRVO)	Q4 2019	56.39%
Companhia Paranaense de Energia Pref ADR (ELP)	Q4 2019	54.19%

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