Sixteen patients with the diagnosis of vertebral or basilar artery dissection who were admitted at the Seoul National University Hospital from 1972 to 1996 are described. During the same period, we encountered 76 patients with posterior circulation aneurysms, so the vertebrobasilar artery dissection was 21% of posterior circulation aneurysms. The mean age was 44 years, and male predominated. Nine patients presented with subarachnoid hemorrhage (SAH) and seven with ischemic symptoms. The characteristic angiographic finding of patients with SAH was aneurysmal dilatation (pseudoaneurysm) in eight of nine cases. In cases of ischemic symptoms, only one case had aneurysmal dilatation. Some other angiographic findings were demonstrated such as string sign, tapered narrowing, complete occlusion, or double lumen. Clinical course of SAH group was much different from that of ischemic group. Rebleeding occurred in three patients of SAH group; immediately after the rebleeding all patients became comatose, but after extraventricular drainage, all patients with rebleeding recovered rapidly. In SAH group, four of nine cases died but there was no mortality in the ischemic group. These four patients showed signs of stem failure, when computed tomography (CT) demonstrated no evidence of additional bleeding and follow-up CT showed the infarction at a part of stem and/or cerebellum. Vasospasm or sudden extensive extension of dissection could be the cause of death. Surgical management was performed in three patients, endovascular intervention in four, and conservative management in two. The patients with incomplete embolization or conservative management had poor outcome. In ischemic group, all underwent conservative management including anticoagulation and/or antiplatelet therapy. On follow-up, most of the patients with ischemic symptoms made complete or very good recoveries.