Moyamoya disease as a clinical entity has been known for more than 40 years. Constant efforts have been directed at clarifying the pathogenesis of this disorder and improving therapeutic methods for the ischemic and hemorrhagic stroke caused by the characteristic vasculopathy of this disease. Although much knowledge has been gained, unresolved problems remain, such as the true epidemiology of this disease, elucidation of the genetic mechanism, and prevention of repeated hemorrhagic events. In this paper, we review recent progress and discuss the outlook for this disorder.