Eleven hundred and sixty-nine young women were prospectively examined for the presence of mitral-valve prolapse as manifested by midsystolic non-ejection click or late systolic murmur (or both). Of the 1169 women 74 (6.3%) had physical findings consistent with mitral-valve prolapse. Sixty-eight of the 74 (92%) had midsystolic non-ejection click, and in 57 the click was accompanied by a late systolic murmur. In six (8%) only a late systolic murmur was heard. Echocardiography on all patients with clinical diagnosis of mitral-valve prolapse showed patterns of prolapse in 60 of 74 (81%). Fourteen (19%) had negative echocardiograms. We conclude that mitral-valve prolapse is clinically present in approximately 6.3% of otherwise healthy young women.