BACKGROUND: Diabetes mellitus is a major cause of coronary artery disease. Despite improvement in the management of patients with stable coronary artery disease, diabetes remains a major cause of increased morbidity and mortality. Although coronary artery bypass grafting surgery (CABG) and percutaneous coronary intervention are widely used, no conclusive evidence exists that either treatment modality is better than medical therapy alone for the treatment of stable single- or multivessel coronary disease in patients with diabetes. METHODS: We compared medical therapy, percutaneous coronary intervention, and CABG in 499 diabetic patients (38.5%) and 799 nondiabetic patients (61.5%) with single- or multivessel coronary disease. The composite primary endpoint was cardiac-related death, Q-wave myocardial infarction, or refractory angina requiring revascularization. RESULTS: We treated 1,298 patients with either CABG (n = 524), percutaneous coronary intervention (n = 378), or medical therapy (n = 396). More deaths occurred among patients with diabetes than among patients without diabetes, regardless of which option was used (p < 0.001). When treatment modalities were stratified according to the number of diseased vessels, CABG was shown to be more beneficial for patients with diabetes and multivessel disease than for patients with diabetes and single-vessel disease (p < 0.001). However, when stratified by treatment, patients with diabetes receiving medical therapy had a worse prognosis than patients with diabetes treated with CABG (p = 0.005). CONCLUSIONS: All three therapeutic regimens resulted in high rates of cardiac-related deaths among patients with diabetes compared with patients without diabetes. Moreover, we observed better outcomes among patients with diabetes and multivessel coronary artery disease undergoing CABG regarding the primary endpoint at 5-year follow-up.