Eleven patients with lesions of the internal carotid and middle cerebral arteries that could not be treated by direct approach are presented. Major vessel occlusion was chosen as definitive therapy. Prophylactic extracranial-intracranial bypass was employed in an attempt to reduce the incidence of ischemic complications. Emphasis is placed on complications, from which several important lessons were learned. Our best results occurred in patients with carotid artery lesions treated with bypass and immediate internal carotid ligation. We believe this to be an effective and safe mode of therapy in cases in which direct approach is not feasible. The low risk and high potential benefit of prophylactic bypass justifies its use before major vessel occlusion in selected cases.