Selected patients with acute or continuing ischemic symptoms from occlusions or inaccessible stenotic lesions of the internal carotid artery or middle cerebral artery have been considered candidates for a carotid artery-middle cerebral artery bypass procedure at our institution since July 1974. We report herein an 8-year experience through June 1982 with 415 operations in 403 patients in whom a branch of the superficial temporal artery was anastomosed to a branch of the middle cerebral artery. Patients selected for operation usually had had more than one form of ischemic symptom. The primary indication for operation was transient ischemic attacks, and the most common vascular pathologic condition was internal carotid artery occlusion. Preoperatively, 183 patients were taking antiplatelet agents and 157 were taking anticoagulants. Neurologic function 6 months postoperatively was equal to or better than the function preoperatively in 95% of survivors. The bypass pedicle was patent in 99% of patients studied. The mortality and morbidity associated with the surgical procedure varied on the basis of the patient's preoperative neurologic condition but were 1% and 4%, respectively, for the entire group at 30 days postoperatively. Of the 54 deaths during the entire follow-up period, 27 were cardiogenic and 6 were from ischemic stroke. On the basis of patient-months of follow-up, stroke was 8 times more likely to occur within 6 months after operation than thereafter.