BACKGROUND: Direct surgical intervention to treat ruptured cerebral aneurysms in patients with moyamoya disease has rarely been attempted and few of these patients have demonstrated full recovery following treatment. METHODS: To clarify the particular operative problems encountered in performing aneurysmal surgery in patients with moyamoya disease, we present two cases and review 10 cases in the literature. RESULTS: The first patient had a newly formed internal carotid artery aneurysm, which enlarged within a period of approximately 2 years. The second patient had multiple basilar artery aneurysms. Both patients had their aneurysms successfully clipped and were discharged without any neurologic deficits. CONCLUSIONS: Aneurysmal surgery in moyamoya disease presents three problems unlike those encountered in uncomplicated aneurysmal surgery: (1) the ordinary approach is prohibited by the presence of moyamoya vessels, (2) careful consideration is required to preserve collateral circulation, and (3) acute surgery is necessary to prevent cerebral vasospasm due to massive subarachnoid hemorrhage.