Objectives: Patients undergoing coronary artery bypass grafting often have untreated mild to moderate mitral regurgitation. The long-term outcome of these patients follows an uncertain course. The purpose of this study was to examine the late outcomes in patients with mild to moderate mitral regurgitation at the time of isolated coronary artery bypass grafting. Methods: One hundred sixty-three patients with mild to moderate mitral regurgitation at the time of isolated coronary artery bypass grafting were identified from the prospectively collected cardiovascular database at Sunnybrook and Women's College Health Sciences Centre. These patients were matched 1:2 with patients who had isolated coronary artery bypass grafting without mitral regurgitation according to gender, age, left ventricular ejection fraction, New York Heart Association functional class, vascular disease, diabetes, extent of coronary disease, and year of surgery. There was 99% complete follow-up. Actuarial survival and event-free (death, myocardial infarction, stroke, cardiac hospitalization, and cardiac reintervention) survivals were compared by log-rank methods. Cox regression was used to assess the effects of the presence of mitral regurgitation on late survival and event-free survival. Preliminary, postoperative follow-up echocardiography was available for 49 of the 163 patients with mitral regurgitation. Results: There were 489 patients in the matched-cohort study, 163 with mitral regurgitation and 326 without. The average length of follow-up was 3.37 ± 2.04 years. There was no difference in actuarial survival at 6 postoperative years (mitral regurgitation 81.0% vs no mitral regurgitation 84.7%, P = .9185). Event-free survival at 6 years was worse in the mitral regurgitation group (45.7% vs no mitral regurgitation 64.7%, P = .0258). Patients with mitral regurgitation had worse functional status (New York Heart Association class 3-4 20.0%, n = 30/150, vs no mitral regurgitation 8.1%, n = 25/307, P = .0046). After the matched variables were controlled for, the hazard ratios associated with the presence of mitral regurgitation by Cox regression were 0.958 (P = .7626) for survival and 1.198 (P = .0333) for event-free survival. The only other significant predictor of late survival was preoperative intra-aortic balloon pump insertion (hazard ratio 2.484, P = .0365). Of the patients who underwent follow-up echocardiography, 30.6% (n = 15/49) had progression of mitral regurgitation to moderate to severe degree at an average of 16.4 postoperative months. Conclusion: Overall late survival was not affected by the presence of mild to moderate degrees of mitral regurgitation in patients undergoing coronary artery bypass grafting. However, these patients had poorer event-free survival and worse late functional status. In a subset of patients with echocardiographic follow-up, the postoperative course of mitral regurgitation was variable, and nearly a third of these patients had worsening mitral regurgitation. Consideration should be given to repairing moderate mitral regurgitation in selected cases to improve long-term quality of life.