Advances in the study of cerebrovascular disease suggest that many risk factors for stroke are under genetic influence. Epidemiologic studies show that parental and sibling histories of cerebral ischemic events are associated with an increased risk of stroke. Explanations for familial stroke aggregation include differential phenotypic expression of apolipoprotein (a) and apolipoprotein E, racial variations in the distribution of vascular disease, identification of the autosomal-dominant disorder cerebral autosomal-dominant arteriopathy with subcortical infarcts and leukoencephalopathy, specific point mutations in the mitochondrial-related disorders, and identification of the clinical significance of hereditable coagulopathies. Greater understanding of these factors may lead to early recognition of and intervention in stroke.