The authors report two siblings, both of whom had unruptured cerebral aneurysms found by screening examination of noninvasive cerebral computed angiotomography. Other authors have reported unruptured cerebral aneurysms detected by conventional cerebral angiography in asymptomatic relatives of families in which two or more individuals had cerebral aneurysmal rupture. It is of interest that, in our cases, the unruptured cerebral aneurysms were detected by noninvasive cerebral computed angiography in two asymptomatic siblings in a family with no history of ruptured aneurysm. To the best of our knowledge, this is the first report of detection of unruptured familial aneurysm by cerebral computed angiotomography. Case 1 is a 67-year-old female who had been complaining of dullness in the head. Cerebral computed angiotomography showed a small high density nodule, suggesting an unruptured aneurysm of the right middle cerebral artery. An aneurysm with a diameter of 4 mm was found in the right middle cerebral artery. A 72-year-old male, who was a brother of case 1, had been afraid of having cerebrovascular disease, and wanted to have a neurological examination check-up. Computed angiotomography revealed a high-density nodule in the anterior communicating artery. Conventional cerebral angiogram showed a 6 X 7 mm aneurysm. However, both of the patients refused surgical treatment. Lozano et al reviewed the previously reported familial aneurysm cases. According to them, familial aneurysm tends to rupture at a younger age and at a smaller size than non-familial aneurysm. It is well known that asymptomatic members of familial aneurysm have a risk of developing aneurysm.(ABSTRACT TRUNCATED AT 250 WORDS)