Commonly used echocardiographic criteria for mitral valve prolapse (MVP) include a sizable proportion of persons whose hearts are normal. Nevertheless, the echocardiogram is generally used as an independent standard for the diagnosis of MVP despite lack of consensus on the criteria to be used and the probability of interobserver variability. Conversely, there is a relatively uniform consensus that classic auscultatory signs establish the diagnosis of MVP beyond reasonable doubt. Accordingly, in 148 patients referred for evaluation of known or suspected MVP, the echocardiographic patterns that coincide with diagnostic auscultatory signs were studied prospectively to compare those patterns with criteria commonly used for the echocardiographic diagnosis of MVP and to determine interobserver variability in echocardiographic interpretation. Eighty patients (54%) had a classic mid- to late systolic click or an apical late systolic murmur, or both. Eleven patients (7%) had the apical holosystolic murmur of mitral regurgitation with no discernible clinical or echocardiographic cause other than the consideration of MVP. Doppler echocardiography was performed in 80 of the 148 patients. The degree of superior systolic bowing of each mitral leaflet and the location of leaflet coaptation relative to the presumed plane of the mitral anulus were graded on apical 4-chamber and parasternal long-axis views. The only patterns absolutely specific for auscultatory MVP were: severe bowing of the anterior or posterior leaflet; coaptation of leaflets on the left atrial side of the anular plane; moderate to severe Doppler mitral regurgitation accompanied by any degree of leaflet bowing; and mild Doppler mitral regurgitation accompanied by moderate bowing of a leaflet.(ABSTRACT TRUNCATED AT 250 WORDS)