Japanese neurosurgeons have recently noticed that there are particular Japanese cases whose cardinal symptoms are characterized by motor paresis or apoplectic stroke. Angiographic findings are most characteristic, demonstrating stenosis or occlusion of the bilateral internal carotid arteries at the site of carotid siphon (C1) and abnormal hemangiomatous vascular network at the base of the brain. 9 cases of the Japanese has been experienced in our clinic. The author reviewed similar cases from literature and letter inquiry which has been made to all of the neurological clinics in Japan. Then, clinical manifestations of the disease have been elaborated on total 118 cases. 1) Sex and Age: 47 were male and 71 were female. The disease was started from under 15 years or less of age in 77 cases. The cases, which had juvenile onset, showed characteristic clinical features. Therefore, such cases will be referred to as juvenile form and the other adult form. 2) Cardinal symptoms were similar to initial ones. Motor paresis was seen in 59 cases out of 77 cases of juvenile form, while subarachnoid hemorrhage was seen in 20 cases out of 41 cases of adult form as an initial clinical symptom. 3) Prognosis: There has been reported frequent recurrence of the symptoms in period of observation of the patients. The recurred symptom disappeared by itself, so no marked progress was noted in the majority of cases. However, some juvenile cases showed progression of symptoms, and death occured in 4 cases out of 77 cases. 4) Sibling incidence was detected in 8 cases (4 couples) out of all the cases. 5) EEG findings: Background activity of EEG ranged from normal to mild slow wave pattern in resting record. Hyperventilation provoked generalized slow wave easily, which continued persistently after the cessation of it in most of the cases. 6) Sex chromosomes were investigated in two female and one male of authors'own cases but no abnormality was noted. 7) 5 autopsy cases were reviewed. The pathological findings brought no contribution to the pathogensis of the disease. 8) Angiographic examination, which was carried out at different period of time, revealed steady appearance of abnormal vascular network in the majority of case of adult form. The patients of juvenile form, who had progression of their symptoms, showed smaller vascular network at the base of the brain. 9) There has been no report of the case upon the foreign race up to the present time. The reports by W. Weidner and N. E. Leed were on the case of Japanese-American woman, American-born Japanese boy and girl. It is the opinion of the author that this disease would be a particular type of cerebral vascular abnormality of the Japanese and that the etiology of this disease is congenital malformation of cerebrovascular system because of bilateral and symmetrical vascular abnormality, existence of sibling cases and resemblance to embryonal vascular system. 10) It should be stressed for the diagnosis of the disease that serial bilateral carotid and vertebral angiography is absolutely necessary to distinguish it from other occlusive diseases of internal carotid artery.