Stroke is an important clinical problem because of its large contribution to mortality. The main causal and treatable risk factors for stroke include hypertension, diabetes mellitus, dyslipidemia, and smoking. In addition to these risk factors, recent studies have shown the importance of genetic factors and interactions between multiple genes and environmental factors. Genetic linkage analyses of families and sib-pairs as well as candidate gene association studies have implicated several loci and many candidate genes in predisposition to ischemic stroke, intracerebral hemorrhage, or subarachnoid hemorrhage. Recent genome-wide association studies identified various loci and genes that confer susceptibility to ischemic stroke or intracranial aneurysm. Such studies may provide insight into the function of implicated genes as well as into the role of genetic factors in the development of ischemic stroke, intracerebral hemorrhage, or subarachnoid hemorrhage.