To clarify the perioperative stroke risk in patients with carotid stenosis or occlusion having coronary artery bypass graft (CABG) surgery, we retrospectively reviewed the records of 1,022 patients who had CABG during a 2-year period (1992, 1993). Of these, 224 had preoperative carotid duplex studies, usually for bruit or remote symptoms. We analyzed clinical and neuroimaging findings for all patients who had strokes to determine infarct topography and presumed mechanism, either low perfusion or embolism. Perioperative stroke was always ipsilateral to severe (> or = 70%) carotid disease, and occurred in 2 (8.0%) of 25 patients with carotid occlusion, 3 (50.0%) of 6 patients with 70 to 99% stenosis, and 9 (4.7%) of 193 patients with less than 70% stenosis. Borderzone infarcts occurred with all degrees of carotid stenosis. Stroke frequency had a positive correlation with the degree of carotid stenosis. Eight (1.0%) of the 798 patients not studied by carotid duplex had stroke in various vascular distributions. Overall, stroke occurred in 22 (2.2%) of the 1,022 patients having CABG surgery. Our results suggest that while the overall risk of perioperative stroke in CABG surgery is low, the risk is increased in patients with severe extracranial carotid stenosis or occlusion. The role of carotid disease and the mechanism of borderzone infarction in CABG surgery remain unsettled.