Seven cases of moyamoya disease accompanied by an aneurysm were studied. The patients, two males and five females, were 13 to 57 years old (average, 32). The cases were classified into two groups: Group A (five cases), in which the aneurysm was located within the moyamoya vessels, and Group B (two cases), in which the aneurysm was located within the circle of Willis and remote from the moyamoya vessels. In all Group A cases, the presenting episode was intracerebral and intraventricular hemorrhage due to rupture of the aneurysm. One patient suffered two separate attacks. In this case, the aneurysm disappeared spontaneously. In one of the two Group B cases, there was hemorrhage from an anterior communicating artery aneurysm. In the other case, with a basilar-superior cerebellar artery aneurysm, there was hemorrhage from the moyamoya vessels.