The diagnosis or exclusion of mitral valve prolapse is one of the most common challenges presented to any echocardiographic laboratory. Implicit in the request that the echocardiographer diagnose prolapse is that 1) Mitral valve prolapse is a defineable anatomic abnormality; 2) the echocardiographer can separate patients with this abnormality from normals based on reasonable, generally accepted crite-ria; and 3) the diagnosis will have sufficient impact on patient management to justify the cost of the test. Given that each of the above are correct, then echocardiography clearly offers an ideal method for diagnosing mitral prolapse in that it permits noninvasive visualization of both mitral leaflets in a variety of projections under basal conditions and in response to stress. It further permits the relationship of the valve leaflets to surrounding structures to be established and quantitative spatial relationships defined.