OPTIMIZERx (OPRX) had the highest return between 1998 and 1999 by a small-cap US stock, returning 1,600%.

ASSET	YEARS	% RETURN
OPTIMIZERx (OPRX)	1998-1999	1,600%
Harmonic (HLIT)	1998-1999	1,587.78%
Smith & Wesson Brands (SWBI)	1998-1999	1,524.69%
Magic Software Enterprises (MGIC)	1998-1999	1,403.02%
Forward Air (FWRD)	1998-1999	1,188.01%
NeoGenomics (NEO)	1998-1999	650%
Acacia Research (ACTG)	1998-1999	648.43%
Kopin (KOPN)	1998-1999	390.52%
Daktronics (DAKT)	1998-1999	380.92%
CTS (CTS)	1998-1999	374.16%
BioCryst Pharmaceuticals (BCRX)	1998-1999	321.43%
Gilat Satellite Networks (GILT)	1998-1999	318.5%
Progress Software (PRGS)	1998-1999	295.93%
SurModics (SRDX)	1998-1999	293.44%
Mitek Systems (MITK)	1998-1999	263.16%
REX American Resources (REX)	1998-1999	245.7%
Sify Technologies (SIFY)	1998-1999	240.66%
LightPath Technologies (LPTH)	1998-1999	225%
Guess? (GES)	1998-1999	216.36%
Heidrick & Struggles International (HSII)	1998-1999	201.78%
ePlus (PLUS)	1998-1999	200%
Bel Fuse A (BELFA)	1998-1999	185.9%
Atlanticus (ATLC)	1998-1999	167.83%
NetScout Systems (NTCT)	1998-1999	158.33%
Bel Fuse B (BELFB)	1998-1999	142.48%

Small-cap stocks are treated as having a market cap between $300M and $2B.