We have performed 10 bypass operations on 7 adult patients with moyamoya disease over the past 6 years. Four had haemorrhagic episodes and three had ischemic episodes. Three patients underwent superficial temporal artery-middle cerebral artery (STA-MCA) bypass on both sides and the other four had the procedure on one side. Six of 7 patients showed angiographical improvement after the bypass operation while one patient did not. This patient underwent the second severe stroke and became vegetative during the course of follow-up. Another patient died of myocardial infarction during the follow-up time. Five patients are capable of carrying out their original work. Considerations regarding the cause, operative methods and disease course in the patients are discussed.