First Solar (FSLR) had the highest return in April 2013 by a large-cap US stock, returning 70.7%.

ASSET	MONTH	% RETURN
First Solar (FSLR)	April 2013	70.74%
Vertex Pharmaceuticals (VRTX)	April 2013	39.67%
Nomura Holdings Inc ADR (NMR)	April 2013	37.65%
Ionis Pharmaceuticals (IONS)	April 2013	29.95%
Tesla (TSLA)	April 2013	27.45%
Celsius (CELH)	April 2013	24.89%
GameStop (GME)	April 2013	24.64%
Orix Corp Ads (IX)	April 2013	24.39%
Akamai Technologies (AKAM)	April 2013	24.14%
Rambus (RMBS)	April 2013	23.84%
Apollo Global Management LLC Class A (APO)	April 2013	22.7%
Lululemon Athletica (LULU)	April 2013	22.14%
Insmed (INSM)	April 2013	21.81%
Sumitomo Mitsui Financial (SMFG)	April 2013	20.43%
Stellantis (STLA)	April 2013	19.81%
Regeneron Pharmaceuticals (REGN)	April 2013	19.52%
Illumina (ILMN)	April 2013	19.4%
Tapestry (TPR)	April 2013	18.24%
Monster Beverage (MNST)	April 2013	18.14%
Deutsche Bank (DB)	April 2013	17.71%
Best Buy (BBY)	April 2013	17.44%
Petroleo Brasileiro Petrobras SA ADR (PBR)	April 2013	17.1%
CGI (GIB)	April 2013	16.57%
AbbVie (ABBV)	April 2013	16.31%
Texas Roadhouse (TXRH)	April 2013	16.16%

Large-cap stocks are treated as having a market cap of $10B+.