In this retrospective clinical analysis for 143 patients who underwent operation due to multiple intracranial aneurysms during the last 12 years(1983-1994), we intended to find out the clinical characteristics, the significant signs for the differentiation between ruptured and unruptured aneurysm, and to compare the results of one-stage operations with those of two-stage operations. The results were s follows; Of 864 patients operated on due to intracranial aneurysms, 143 patients(16.6%) had two or more intracranial aneurysms. Multiple aneurysms were more common in females, with a female to male ratio of 2.4 : 1 as compared with 1.3 to 1 for patients with single aneurysm. Common locations of the aneurysms were the middle cerebral artery, and posterior communication artery, anterior communicating artery, and the anterior choroidal artery, in that order. In identifying the site of rupture, the focal hematoma in brain CT scan, segmental vasospasm, irregularity and sizes of aneurysmal sacs on angiograms were helpful. Aneurysms 3mm or less were less prone to rupture. However, for those with a diameter of more than 4mm, the frequency of rupture increased with the size of aneurysm. Eighty eight percent of patients who underwent operations had a favorable outcome and the operation mortality rate was 7.7%. In patients of Grade I and II, surgical results of the one-stage operation group and two-stage operation group did not differ. In Grade III patients, the results were better for the two-stage operation group, without statistical significance. From our studies we have come to the conclusion that incidental aneurysms found in patients with low risk should be treated at the same time when ruptured aneurysms are clipped.