The authors review the surgical results in 372 cases of multiple intracranial aneurysms during this 25-year period in which one of the authors (JS) performed 2,000 direct operations for aneurysms. All patients were classified into four groups according to the location of aneurysms as follows: 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 vertebrobasilar artery aneurysms (33 cases). In multiple aneurysm cases, their 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 Group 2 were treated by one-stage operations, while 60% of patients in Group 3 and 42% of in Group 4 were operated on in the same manner. Excellent and good results in from 73% to 81% of cases was obtained in patients of Group 1, Group 2 and Group 3. Morbidity was 14-19% and mortality was 6-8%. These results were almost equal 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.(ABSTRACT TRUNCATED AT 250 WORDS)