The proper treatment of multiple and incidental aneurysms remains controversial because the long-term result of different modes of management is unclear. This report evaluates the long-term outcome (follow-up period averaged 7.7 years) in 182 patients with multiple aneurysms who suffered a subarachnoid hemorrhage (SAH) to document the incidence of late bleeding. Of the 182 patients, 132 were treated by bed rest and 50 by surgery (craniotomy) directed at only the ruptured aneurysm. Seventy of the patients with bed rest were alive after 6 months. Twenty-one of these conservatively treated patients (30%) suffered a late hemorrhage, which is equal to the previously reported average yearly rebleed rate (3%) with a single aneurysm of the anterior circulation. There was no evidence that a previously intact aneurysm had ruptured in SAH patients treated with bed rest, indicating that late hemorrhage was due to rerupture from the original aneurysm. Patients who were hypertensive and who had a large aneurysm had an increased risk of late rehemorrhage. A linear discriminant analysis was developed to predict late rebleeding. The fate of intact aneurysms was evaluated by following patients with multiple aneurysms treated by craniotomy directed only at the ruptured aneurysm. Of the 50 craniotomy patients, 38 were alive after 6 months. In this group, the minimal risk of rupture of an intact aneurysm is approximately 1% per year. The presence of hypertension increased the risk of late hemorrhage. In conclusion, patients with multiple untreated aneurysms managed by bed rest have a late rehemorrhage rate equal to that observed in patients with a single cerebral aneurysm; the data indicate that rupture of intact aneurysms is not insignificant.