The present study was undertaken to reach a clearer understanding of the natural history of Moyamoya disease. Follow-up studies were performed in 88 patients with Moyamoya disease. They were divided into the ischemia group and the hemorrhage group. The activity of daily living (ADL) of each groups were followed up and compared between those who were surgically treated and conservatively managed. Ischemic manifestations were more common in the younger children and tended to be recurrent, whereas hemorrhagic manifestations were more common in the adults. Follow-up duration of the 36 patients, who were surgically treated, ranged from 6 to 86.4 months (mean: 28.8 months). During the follow-up period, ADL was improved in 17 of 31 ischemic Moyamoya patients (55%); the condition was unchanged in nine (29%); and aggravated in five (16%). Follow-up duration of the 52 patients who were managed without surgery ranged from 12 to 216 months (mean: 67.2 months). In 35 patients of the ischemia group, ADL was aggravated in 49% and improved in only 26% during the follow-up period. However, ADL was aggravated in 12% of 17 hemorrhagic patients, but improved in 53%. Our result suggest that indirect revascularization procedures are effective for prevention of recurrent ischemic attacks which is common in pediatric patients. However, the effectiveness of indirect revascularization for hemorrhagic Moyamoya disease is not clear and requires extended follow-up study.