The occurrence of unilateral and bilateral moyamoya disease may be associated with intracranial aneurysms. These aneurysms are of two types: major-artery aneurysms and peripheral-artery aneurysms. The former arise at the circle of Willis and the latter are located mainly at either the moyamoya vessels or at the choroidal arteries. We analyzed 76 patients with cerebral aneurysms associated with moyamoya disease who were affected unilaterally or bilaterally. Of them, 10 cases were studied by our group and 66have been reported in other studies. The characteristics of the aneurysms were assessed. The frequency of aneurysms associated with moyamoya is 4-fold higher in unilateral than in bilateral moyamoya. Major-artery aneurysms are found mainly in the arterial complex of the anterior communicating artery-anterior cerebral artery in patients with unilateral moyamoya, and in the basilar artery in patients with bilateral moyamoya. When microaneurysms are taken into account, peripheral-artery aneurysms are more frequent than major-artery aneurysms. Our results suggest that aneurysms associated with moyamoya disease have some characteristics that should be taken into consideration when making comparisons with these lesions encountered in the general population.