Mitral valve prolapse (MVP) is usually a primary, dominantly inherited condition. Diagnosis may be made by auscultation of a midsystolic click and late-systolic murmur that move dynamically with postural maneuvers. Echocardiography confirms the diagnosis by demonstrating M-mode late-systolic prolapse and 2-D leaflet billowing into the left atrium. More severe forms of MVP can be detected echocardiographically by documentation of significant mitral regurgitation, enlargement and thickening of the mitral leaflets and anulus, and loss of leaflet apposition. In contrast to earlier reports, the true "MVP syndrome" consists of low body weight and blood pressure, minor skeletal abnormalities, orthostatic hypotension, palpitations and mitral regurgitation of variable degree. Complications of MVP include progressive mitral regurgitation, infective endocarditis, and possible risk of neurologic ischemia, arrhythmic sudden death, and orthostatic syncope. Risk factors for complications among MVP patients include older age, male gender, the presence of a mitral regurgitant murmur, and, possibly, higher weight and blood pressure. MVP patients with neither a murmur nor Doppler evidence of mitral regurgitation may be reassured that their condition is benign. For other MVP patients, the presence and severity of mitral regurgitation govern the frequency and intensiveness of needed follow-up.