A series of 51 consecutive patients with 55 cerebral aneurysms of the vertebrobasilar system is presented. Thirty aneurysms had their origins at the basilar artery(BA) bifurcation, 7 at the origin of the superior cerebellar artery (SCA), 4 at the posterior cerebral artery(PCA), 4 at the BA trunk, 8 from the vertebral artery(VA) at the origin of the posterior inferior cerebellar artery(PICA), and two from the PICA. The patient population consisted of 31 women and 21 men, with a mean age of 50 years(range 30-70 years). The overall mortality and morbidity rates at 6 months were 17.6%(9/51) and 13.7%(7/51), respectively. The most common cause of death was rebleeding(55.6%, 5/9). Nineteen patients had underwent only conservative treatment due to aneurysms classified as inoperable(6 cases), fatal rebleeding(5 cases), refusal against surgery(5 cases), poor Hunt and Hess grade that did not improve(2 cases), and one aneurysm that spontaneously disappeared. Treatments consisted of neck clipping in 16 patients, wrapping in 6, and endovascular therapy in 10. All of these treatment modalities were carried out after 2 weeks from initial insult. Treatment outcome was evaluated with Glasgow Outcome Scale(GOS) at 6 months after initial insult. Patients with Hunt and Hess(H-H) Grades I and II at admission had good outcome in 70.6%, whereas only 60% of patients with H-H Grades III and IV showed good outcome. But there was no statistically significant difference. Five patients with aneurysms which were located proximally had better outcome than those with distal aneurysm(100% good outcome vs 66.7%). All of ten patients who were treated with endovascular therapy showed good outcome, whereas only 13 out of 22(59.1%) patients who underwent either clipping or wrapping showed good outcome. There was statistically significant difference(p<0.05). As for the comparison of outcome according to the size of aneurysm and age of patients, we found no statistically significant difference. These results indicated that the location of aneurysm was one of important prognostic factor in vertebrobasilar system. Endovascular treatment may be a promising treatment option and considering the very high mortality from rebleeding early management may contribute to reduce the mortality and morbidity in posterior circulation aneurysm.