Mitral valve prolapse (MVP), which occurs in about 3% of adults, is usually a primary, dominantly inherited condition. MVP may be diagnosed by auscultation of a mid-systolic click and late-systolic murmur that move dynamically with postural maneuvers. M-mode echocardiography confirms MVP by demonstrating late-systolic prolapse and two-dimensional echocardiography reveals leaflet billowing into the left atrium. Echocardiography identifies severe forms of MVP by documenting significant mitral regurgitation, enlargement and thickening of the mitral leaflets and annulus, and loss of leaflet apposition. In contrast to early reports, true "MVP syndrome" as revealed by controlled studies consists of low body weight and blood pressure, minor skeletal abnormalities, orthostatic hypotension, palpitations, and mitral regurgitation that is usually mild. Complications of MVP include progressive mitral regurgitation, infective endocarditis, orthostatic syncope, and possible risks of neurologic ischemia and arrhythmic sudden death. Risk factors we have identified for complications among patients with MVP include older age, male gender, the presence of mitral regurgitation, and possibly, higher weight and blood pressure. The cumulative risk of all complications of MVP by age 75 is from 5% to 10% for affected men and 2% to 5% for affected women. Patients with MVP who have neither a murmur nor Doppler evidence of mitral regurgitation may be reassured that their condition is benign. For other patients with MVP we have shown that oral antibiotic prophylaxis is cost-effective. The presence and severity of mitral regurgitation govern the frequency and intensiveness of follow-up.