Moyamoya disease is an idiopathic disorder characterized by progressive occlusion of the internal carotid and anterior and middle cerebral arteries, with formation of an extensive abnormal collateral circulation at the base of the brain. Many neurosurgical procedures have been designed to bypass these occluded vessels. The results of one of these procedures, modified encephaloduroarteriosynangiosis was reviewed in five children followed for 3 1/2 to 19 1/2 years. Modified encephaloduroarteriosynangiosis performed unilaterally in one and bilaterally in four of the children, appeared to halt neurologic deterioration, despite angiographic progression, in four of the five children.