OBJECTIVES Atrial fibrillation (AF) is associated with less favorable outcomes in patients undergoing mitral valve and tricuspid valve surgery. Despite growing evidence on the potential benefits of surgical ablation for AF there is significant variability among surgeons in treatment of AF. The purpose of our study was to assess the effect of the Cox-maze procedure on operative and follow-up outcomes. METHODS In our prospective study, patients who underwent isolated mitral valve or mitral valve+tricuspid valve surgery without history of AF (n = 506), with untreated AF (n = 75), or with Cox-maze procedure (n = 236) were included (N = 817). Sinus rhythm was captured according to Heart Rhythm Society guidelines. Patients who underwent the Cox-maze procedure were propensity score matched to patients without history of AF resulting in 208 pairs of patients. RESULTS Operative outcomes were comparable after propensity score matching (Cox-maze procedure vs no AF) stroke/transient ischemic attack (0.5% vs 0.5%; P = 1.00), renal failure (2.9% vs 1.4%; P = .34), and operative mortality (1.4% vs 1.4%; P = 1.00). High return to sinus rhythm was documented at 6, 12, and 24 months (92%, 91%, and 86%, respectively) as well as sinus rhythm off antiarrhythmic drugs (79%, 84%, and 82%, respectively). Incidence of embolic stroke in patients who underwent Cox-maze procedure was 1.7% (4 out of 232 patients) and 5.1 cases per 1000 person-years. No difference in 4-year cumulative survival between propensity score-matched groups (91.9% vs 86.9%; log rank, 1.67; P = .20), but higher for patients who underwent Cox-maze procedure versus patients with untreated AF (hazard ratio, 2.47; P = .048). Higher additive European System for Cardiac Operative Risk Evaluation (odds ratio, 1.40; P < .001) and limited surgeon experience with Cox-maze procedure (odds ratio, 3.60; P < .001) were significant predictors for failure to perform Cox-maze procedure. CONCLUSIONS In our center, 76% of patients undergoing mitral valve or mitral valve+tricuspid valve surgery experiencing AF underwent concomitant Cox-maze procedure, which is considerably higher than the national average. No increased morbidity was associated with the Cox-maze procedure with the benefit of very low thromboembolic rate. These results suggest the need for performance-based education for AF surgical ablation to achieve optimal outcomes.