Echocardiographic studies were performed on 134 consecutive patients with idiopathic mitral valve prolapse syndrome. Fifteen patients (11.2%) were noted to have ruptured chordae tendineae on M-mode examination and in 12 of them the diagnosis was confirmed by bidimensional studies. Only four patients were referred for surgery as a result of severe mitral regurgitation. At operation one patient was found to have rupture of the anterior mitral chorda and the other three had posterior mitral chordal rupture. Eleven patients with chordal rupture had either mild symptoms or were completely asymptomatic. It is concluded that chordal rupture in patients with the mitral valve prolapse syndrome does not always result in severe hemodynamic deterioration and may go undetected unless a high index of suspicion is maintained. Serial echocardiographic studies may reveal the natural history of this condition in asymptomatic patients.