We retrospectively reviewed the CT scans and angiograms of 17 cases with angiographically-proved moyamoya disease from April 1987 to October 1989. The results were as follows. 1. The age distribution ranged form 9 48. Eight patients were less than 20 years old. 2.Nine cases were male and 8 cases were female. 3. On postcontrast CT scan, curvilinear. tortuous vessels were well dilineated at the circle of willis and basal ganglia in 4 cases, and cortical enhancement in 7 cases. These findings are most likely to represent parenchymal and leptomeningeal collateral vessels on angiography. 4. On angiography, bilateral supraclinoid internal carotid artery(ICA), proximal middle cerebral artery(MI), and proximal anterior cerebral artery(AI) were involved in 13 cases. 5.The prognosis was poor in one case with bilateral ICA, MI, AI, and posterior cerebral artery(PCA) involvement. 6.One case had a pseudoaneurysm which was seen at the left anterior choroidal artery branch, and measured about 3x2mm in size. 7.One case was accompanied by a dural arteriovenous malformation(AVM).