Endovascular occlusion of vertebral arteries in the treatment of unclippable vertebrobasilar aneurysms. Twenty-one patients with aneurysms of the vertebrobasilar circulation underwent unilateral or bilateral endovascular occlusion of the vertebral artery. Six patients presented with subarachnoid hemorrhage (SAH), 10 with mass effect, four with mass effect and SAH, and one with ischemic symptoms. Thirteen patients had good outcomes with complete clinical and angiographic cure. Six patients had partial thrombosis of their aneurysms. There was one death and one treatment failure. One patient suffered transient stroke. It is concluded that endovascular occlusion of the vertebral artery following test occlusion is a safe and effective treatment for proximal aneurysms of the vertebrobasilar circulation. 