Several studies indicate a high prevalence of factor V Leiden mutation as the most frequent coagulation defect found in patients with venous thrombosis. The relationship between this mutation and cerebrovascular disease has not been established in adults. In this investigation, we studied 29 patients with ischemic stroke and 20 with intracerebral hemorrhage, all of whom were compared with 20 controls. A region of the factor V gene containing the Leiden mutation site was amplified with polymerase chain reaction and the presence of mutation was determined with restriction enzyme digestion. We found no evidence of an association between factor V Leiden mutation and ischemic stroke or intracerebral hemorrhage. There was no evidence of association in subgroup the analysis by age, smoking status, myocardial infarction, hypertension, diabetes mellitus, or coronary disease. Factor V Leiden mutation doesn't seem to be associated with a risk of cerebrovascular disease.