OBJECTIVE To determine the frequency of risk factors and the mechanisms of stroke in patients with cerebral infarction and echocardiographically diagnosed mitral valve prolapse in the general population. DESIGN We conducted a population-based study in Olmsted County, Minnesota, which encompassed the period from 1975 through 1989. MATERIAL AND METHODS Study subjects were identified by using the Rochester Epidemiology Project medical records-linkage system. Cardiac and neurologic data were summarized, and a two-sided chi 2 test or Fisher's exact test was used for statistical analysis. RESULTS Among residents of Olmsted County, Minnesota, 33 had echocardiographically diagnosed mitral valve prolapse and a first cerebral infarction between 1975 and 1989. The mean patient age was 71 years, and more than half (52%) were men. Risk factors for stroke included hypertension (55%), smoking (42%), coronary artery disease (27%), atrial fibrillation or flutter (24%), congestive heart failure (21%), hypertensive heart disease (21%), prior myocardial infarction (12%), diabetes (9%), and sick sinus syndrome (3%). Cerebral infarction subtypes were as follows: cardioembolic source (excluding mitral valve prolapse only), 30%; lacuna, 12%; large-vessel atherosclerosis, 9%; other, 6%; and infarction of uncertain cause (including mitral valve prolapse), 42%. CONCLUSION Most Olmsted County patients with cerebral infarction and echocardiographically diagnosed mitral valve prolapse had other risk factors for stroke, and most had identifiable mechanisms of infarction other than embolism due to mitral valve prolapse.