We review the surgical results in 372 cases of multiple intracranial aneurysms over a 25-year period in which one of us (JS) performed 2,000 direct operations for aneurysms. All patients were classified into four groups according to the location of the aneurysm: Group 1: multiple aneurysms including anterior communicating artery aneurysm (157 cases); Group 2: multiple aneurysms of unilateral anterior circulation (72 cases); Group 3: multiple aneurysms of bilateral anterior circulation (110 cases); Group 4: multiple aneurysms including vertebro-basilar artery aneurysms (33 cases). In multiple aneurysm cases, our policy has been to treat all aneurysms, ruptured and unruptured, in a one-stage operation whenever possible. About 90% of patients in both Group 1 and 2 were treated by one-stage operations, while 60% of patients in Group 3 and 42% of patients in Group 4 were operated on in the same manner. Excellent and good results in from 73% to 81% of cases were obtained in patients in Group 1, Group 2 and Group 3. Morbidity was 14-19% and mortality was 6-8%. These results were comparable to the results with a single aneurysm of the anterior circulation. On the other hand, the surgical results in Group 4 were poor with a mortality of 27%. Poor results were attributable to the postoperative rebleeding from the untreated vertebro-basilar aneurysms, which were thought to be unruptured aneurysms preoperatively. Furthermore, it was clarified that the results of early one-stage operations (within one week from onset) in patients with multiple aneurysms were satisfactory. In this group, there was good recovery in 84% of patients, 7% were disabled and 9% died.(ABSTRACT TRUNCATED AT 250 WORDS)