BACKGROUND- Moyamoya disease (spontaneous occlusion of the circle of Willis) is a rare disease, previously thought to be confined to Japan and other Asian countries, but now known to occur worldwide, although at a lower frequency. Information about its correct diagnosis and appropriate treatment is frequently requested, especially in Europe and the United States.REVIEW SUMMARY- The clinical features of Moyamoya disease are now well established, as is its treatment, which is directed against cerebral ischemia. It is possible that Asian, American, and European patients differ in some ways in the clinical expression of the disease. Similar clinical features associated with other systemic diseases should be referred to as Moyamoya syndrome, rather than Moyamoya disease. The prognosis with regard to life expectancy is relatively favorable, but the associated impairment of intellectual development is currently drawing more attention. Revascularization procedures reportedly improve the prognosis in this regard. The optimal choice of revascularization procedure remains under discussion. Recent scientific developments include the application of molecular biological techniques, such as testing for basic fibroblastic growth factor in the vascular wall and in the cerebrospinal fluid, and genetic analysis of familial cases, which account for approximately 10% of all cases, in the search for the still unknown etiology of the disease.CONCLUSION- The principal clinical manifestations of Moyamoya disease are cerebral ischemia in children and in-tracranial bleeding in adults. These are caused by the severe stenosis or occlusion of the internal carotid artery at its terminal portion bilaterally, which induces the formation of abnormal vasculature (Moyamoya) in the basal ganglia. It is treated by the administration of aspirin to prevent progression of the disease and by a revascularization procedure to augment the cerebral blood flow.