The occurrence of stroke associated with coronary artery bypass operations is approximately 2%. In an attempt to reduce this incidence some centers have proposed carotid thromboendarterectomy for symptomatic and asymptomatic carotid arterial disease in patients undergoing a coronary artery bypass operation. To obtain a better understanding of the incidence of carotid occlusive disease in candidates for the coronary bypass operation and to evaluate the practical use of a noninvasive method to screen patients preoperatively, we evaluated 102 patients preoperatively with an ultrasonic Duplex scanner; 24 studies were requested on the basis of either previous neurologic problems or the presence of a bruit and 78 patients were evaluated as part of a study protocol. In the unrequested group 6% (5/78) of the patients had a stenosis of 50% diameter reduction or more. In the requested group 54% (13/24) had a stenosis of 50% diameter reduction or more. In the postoperative phase one stroke and one transient ischemic attack were noted among the unrequested group and none in those suspected of having carotid disease on clinical grounds. Neither affected patient had a high-grade stenosis. There is little evidence to support the contention that noninvasive screening of patients free of symptoms or signs of carotid disease prior to coronary artery bypass operation is a valuable method of screening for patients who will sustain a focal neurologic event.