A system of grouping patients according to preoperative evaluation of risk of carotid endarterectomy is presented. The primary complications of this surgical procedure were myocardial infarction and residual mild to severe neurologic deficit. Neurologically stable patients without medical or angiographically determined risk factors (group 1, 129 patients) have a risk of 1%. Neurologically stable patients without medical risk but with angiographically determined risk (group 2, 56 patients) have a risk of 2%. Neurologically stable patients with significant medical illness and with or without angiographically determined risks (group 3, 76 patients) have a risk of 7%, primarily related to cardiac disease. Neurologically unstable patients (group 4, 70 patients) have a 10% risk for a neurologic deficit.