Moyamoya disease (MMD) is a progressive occlusive disease of the cerebral vasculature with particular involvement of the circle of Willis and the arteries that feed it. MMD is one of cerebrovacular accident,which is treated with sugical maeuver in pediatic neurosurgery. Moyamoya (ie, Japanese for "puff of smoke") characterizes the appearance on angiography of abnormal vascular collateral networks that develop adjacent to the stenotic vessels. The steno-occlusive areas are usually bilateral, but unilateral involvement does not exclude the diagnosis. The exact etiology of moyamoya disease is unknown. Some genetic predisposition is apparent because it is familial 10% of the time. The disease may be hereditary and multifactorial. It may occur by itself in a previously healthy individual. However, many disease states have been reported in association with moyamoya disease, including the following: 1) Immunological - Graves disease/thyrotoxicosis 2) Infections - Leptospirosis and tuberculosis 3) Hematologic disorders - Aplastic anemia, Fanconi anemia, sickle cell anemia, and lupus 4) Congenital syndromes - Apert syndrome, Down syndrome, Marfan syndrome, tuberous sclerosis, Turner syndrome, von Recklinghausen disease, and Hirschsprung disease 5) Vascular diseases - Atherosclerotic disease, coarctation of the aorta and fibromuscular dysplasia, 6)cranial trauma, radiation injury, parasellar tumors, and hypertension etc. These associations may not necessarily be causative but do warrant consideration due to impact on treatment.(Mainly neurosurgical operation.) The incidence of moyamoya disease is highest in Japan. The prevalence of MMD is 1 person per 100,000 population. The prevalence and incidence of moyamoya disease in Japan has been reported to be 3.16 cases and 0.35 case per 100,000 people, respectively. With regard to sex, the female-to-male ratio is 1.4:1. A bimodal peak of incidence is noted, with symptoms occurring either in the first decade(5-10yr) or in the third and fourth decades (30-40yr)of life. Mortality rates of moyamoya disease are approximately 10% in adults and 4.3% in children. Death is usually from hemorrhage. In aspect of life insurance, MR is 1700%, EDR is 16 per 1000 persons. Children and adults with moyamoya disease (MMD) may have different clinical presentations. The symptoms and clinical course vary widely from asymptomatic to transient events to severe neurologic deficits. Adults experience hemorrhage more commonly; cerebral ischemic events are more common in children. Children may have hemiparesis, monoparesis, sensory impairment, involuntary movements, headaches, dizziness, or seizures. Mental retardation or persistent neurologic deficits may be present. Adults may have symptoms and signs similar to those in children, but intraventricular, subarachnoid, or intracerebral hemorrhage of sudden onset is more common in adults. Recently increasing diagnosis of MMD with MRI, followed by surgical operation is noted. MMD needs to be considered as the "CI" state now in life insurance fields.