The etiology of perioperative stroke in patients undergoing isolated coronary artery bypass grafting (CABG) is multifactorial. One significant cause is thought to be high-grade internal carotid artery stenosis. Between April 1992 and June 1995, 1686 patients undergoing isolated CABG underwent preoperative carotid duplex scanning. This represented 77% of patients who underwent CABG during that time period (2188 patients). Sixty-eight patients (4.0%) had 80%-99% stenosis of at least one carotid artery. Fifteen patients underwent CABG without carotid intervention (Group I) and 53 patients underwent either carotid endarterectomy prior to CABG or simultaneous with CABG (Group II). Age, sex, history of prior neurologic events, ejection fraction, number of distal bypasses performed, total pump time, and aortic cross clamp times were similar between the two groups. Three patients in Group I developed a permanent postoperative neurologic deficit (20%) and one patient developed a transient deficit. The defect was focal and ipsilateral to high-grade stenosis in three patients and global in one. No patient in Group II developed either a transient or permanent neurologic deficit. There was one death in Group I in the patient who developed a global neurologic deficit and one death in Group II 2 weeks after CABG in a patient who had undergone prophylactic preCABG-carotid endarterectomy. Statistical analysis (Fisher's exact test, 2-tail) demonstrated a significant decrease both in total neurologic events (p = 0.001) and permanent neurologic defects (p = 0.005) in those patient undergoing prophylactic CE (Group II). Patients with 80%-99% carotid stenosis undergoing CEA prior to or in conjunction with isolated CABG have a decreased incidence of neurologic events postoperatively.