The management outcome of 302 patients with multiple intracranial aneurysms (MIA) from a series of 1314 patients with cerebral aneurysms was assessed using the Glasgow Outcome Scale 1 year after diagnosis and/or treatment. The outcome was significantly poorer for patients with MIA than for those with single intracranial aneurysms (SIA). The difference in the frequencies of poor outcome (Glasgow Outcome Scale Grades 3-5) was most evident in patients with Hunt and Hess Grades 2 or 3 (MIA, 29%; SIA, 19%). The management mortality in all grades attributable to all causes was 24% in patients with MIA and 20% in those with SIA and 16 and 11%, respectively, after surgery. At the 1-year follow-up point, 66% of the patients with MIA were independent (SIA, 72%); after surgery, 74% (SIA, 81%); after subarachnoid hemorrhage, 65% (SIA, 71%); and after subarachnoid hemorrhage and surgery, 73% (SIA, 80%). Patients with aneurysms at the vertebrobasilar arteries fared badly; otherwise, the sites of the aneurysms and their different combinations had no effect on outcome, nor did the timing of surgery. In this study, again, only two-thirds of the detected aneurysms could be secured. The aneurysms left without treatment were mostly in patients with very poor grade (n, 55) and/or old (n, 23) patients or were intracavernous (n, 26). The results seemed to be more unsatisfactory as the number of aneurysms increased. In multivariate analysis, delayed neurological deficit had the most significant independent contribution to outcome in patients with MIA, far more than in patients with SIA. This can be explained by the increased manipulation of cerebral arteries during multiple aneurysm surgery.