Ten per cent of all patients referred to the echocardiography laboratory for diagnostic evaluation had mitral valve prolapse. Of these 35 patients, 19 (54 per cent) had prolapse of both the anterior and posterior mitral leaflets. Of the 19 patients, 13 had Type A or midsystolic prolapse, whereas six had Type B or pansystolic prolapse of the mitral leaflets. Simultaneous phonocardiographic examination of the patients revealed either midsystolic click and late systolic murmur, pansystolic murmur, or isolated click and short systolic murmur. There was no apparent correlation between the echocardiographic prolapse pattern and the auscultatory events. One patient with Type A prolapse had no auscultatory abnormalities at the time of the examination. It is suggested that the abnormal sounds may be generated by a redundant mitral leaflet rather than chordae tendineae.