It is not easy to evaluate the prognosis of mitral valve prolapse. First of all, a positive diagnosis is difficult: the clinical insufficiencies are ill-compensated by sonocardiography as it is less reliable than expected; the very existence of the "mitral valve prolapse" described by Barlow is being challenged. Secondly, the most severe complications of mitral prolapse are rare, with respect to its frequency. Some complications are currently well defined. Thus, severe mitral insufficiency, leading to valve replacement, affects elderly men more than young women, although the pathological lesions correspond to the same disease. Endocarditis is rare and only occurs when there is an audible murmur. Rhythm disorders are varied, with however, frequent junction tachycardias and a marked influence of catecholamines, which may explain the clinical effectiveness of beta-blockers. Unfortunately, severe complications are not as well known. Thus, the risk of sudden death and cerebral vascular accident cannot be figured out from large statistical studies. Only studies of some so called "risk" sub-groups, should allow a better knowledge of these two complications and a more effective prevention.