All patients 20 years old or older referred for echocardiographic examination and found to have mitral valve prolapse during the period January 1975 through December 1979 were included in the study. Of the 1,138 patients, two-thirds were women and one-third were men. Their average age was 48.4 years. Forty patients (3.5%) had histories of prior focal cerebrovascular ischemic events. In 26 of the 40 patients, no responsible mechanism other than mitra valve prolapse was identified, and in 4, the ischemic event occurred during an episode of bacterial endocarditis, a known complication of mitral valve prolapse. In 10 of the 26 patients, there was clinical information to suggest an embolic mechanism for the ischemic. A conservative estimate of the prevalence rate for cerebral infarction in this group of patients is four times greater than the rate expected in a normal population. This difference is likely due to the contribution of mitral valve prolapse in the pathogenesis of cerebral infarction.