The aim of this study was to characterize patients with and without prior coronary artery bypass grafting (CABG) among a prospectively identified cohort of patients presenting with unstable angina or non-Q-wave myocardial infarction. Patients in the Thrombolysis in Myocardial Infarction phase III Registry Prospective Study presented within 96 hours of an episode of unstable angina or non-Q-wave acute myocardial infarction. Of 2,048 patients, 336 (16.4%) had prior CABG. Compared with those without prior CABG, patients were the same age, but were more likely to be men, white, diabetic, have o history of angina or myocardial infarction, to have received anti-ischemic medications in the prior week, and to receive intravenous heparin or nitroglycerin, or both, during hospitalization. They were equally likely to undergo coronary angioplasty or CABG. Death or nonfatal myocardial infarction occurred by day 10 in 4.5% of patients with prior CABG and 2.8% of patients without prior CABG (p = 0.11); and by day 42 in 7.7% and 5.1%, respectively (p = 0.03). The composite of death, myocardial infarction, or recurrent ischemia at 1 year was more common among patients with prior CABG (39.3% vs 30.2%, p = 0.002). By multiple logistic regression, prior CABG was not independently associated with the occurrence of death or myocardial infarction, or the composite of death, myocardial infarction, or recurrent ischemia either at 6 weeks or at 1 year. The likelihood of recurrent ischemic events is greater among patients with than without prior CABG, but is most likely explained by differences in baseline or treatment characteristics which reflect the degree of underlying cardiac disease.