We evaluated 147 patients with adequate color Doppler and angiographic studies for mitral regurgitation. Sixty-five patients had no mitral regurgitation by both color Doppler and angiography and 82 patients had mitral regurgitation by both techniques. Thus the sensitivity and specificity of color Doppler for the detection of mitral regurgitation was 100%. Three two-dimensional echocardiographic planes (parasternal long and short axis, apical four-chamber view) were used to analyze variables of the mitral regurgitant jet signals in the left atrium. The best correlation with angiography was obtained when the regurgitant jet area (RJA) (maximum or average from three planes) expressed as a percentage of the left atrial area (LAA) obtained in the same plane as the maximum regurgitant area was considered. The maximum JRA/LAA was under 20% in 34 of 36 patients with angiographic grade I mitral regurgitation, between 20% and 40% in 17 of 18 patients with grade II mitral regurgitation, and over 40% in 26 of 28 patients with severe mitral regurgitation. Maximum RJA/LAA also correlated with angiographic regurgitant fractions (r=.78) obtained in 21 of 40 patients in normal sinus rhythm and with no evidence of associated aortic regurgitation. Other variables of the regurgitant jet such as maximal linear and transverse dimensions, maximal area, or maximal area expressed as a percentage of the LAA in one or two planes correlated less well with angiography. Color Doppler is a useful noninvasive technique that is not only highly sensitive and specific in the identification of mitral regurgitation but also provides accurate estimation of its severity.