We performed 956 carotid endarterectomies in 661 conscious patients who were under cervical block anesthesia and in whom the stroke rate was 2.5%. They were analyzed to determine the mechanisms of strokes and the risk factor for perioperative stroke. Twenty-three patients with perioperative strokes, regardless of severity, were analyzed as to the mechanism of cause. One half were due to technical problems, one quarter to intraoperative embolization, one sixth to intracerebral hemorrhage, and the remainder were not directly related to the operative procedures. Perioperative stroke rate varied by group from 0.6% to 28.4%, highest when the contralateral carotid was occluded, where there was a preoperative persistent neurologic deficit, and when the patient failed to tolerate carotid clamping. Regional block monitoring was accurate and no stroke could be ascribed to anesthetic technique. Standard reporting techniques should be used in classifying patients into appropriate risk groups to permit meaningful comparisons among groups using different techniques for cerebral protection.