Because mitral valve prolapse and patent foramen ovale are supposed to promote stroke in young patients, we assessed the frequency of patent foramen ovale in 18 patients younger than 45 years with stroke and mitral valve prolapse diagnosed on echocardiography at the time of stroke, who were admitted to 2 university hospitals. Eleven patients were called back to hospital for contrast transthoracic and/or transesophageal echocardiography, 3 to 7 years after their initial stroke. A patient foramen ovale was found in 9 patients (50%). In 4 re-assessed patients no mitral valve prolapse was found using our present criteria. Six patients with mitral valve prolapse had a patent foramen ovale (43%). Our results suggest that mitral valve prolapse is commonly associated with patent foramen ovale in young stroke patients.