Six cases of unclippable vertebral aneurysms were treated by therapeutic occlusion of the proximal vertebral artery. In three cases, the vertebral artery was clipped proximal to the posterior inferior cerebellar artery (PICA), and all of these patients had a postoperative embolic complication or a fatal subarachnoid hemorrhage. In two cases, the vertebral artery was clipped distal to the PICA and in one case the PICA was absent and the vertebral artery was clipped proximal to the aneurysm. All three of these patients did well without any neurological deficit. Possible mechanisms of the complications are discussed, and the importance of not clipping the PICA is stressed.