The appearance of atrial fibrillation is associated with significant clinical deterioration in patients with obstructive hypertrophic cardiomyopathy; therefore, maintenance of sinus rhythm is desirable. Guidelines and most articles have reported the results of catheter ablation and pharmacologic atrial fibrillation treatment; nevertheless, data regarding concomitant procedures during septal myectomy are limited. The aim of this study was to assess the outcomes of concomitant atrial fibrillation treatment in patients with obstructive hypertrophic cardiomyopathy. Between 2010 and 2013 in our clinic, 187 patients with obstructive hypertrophic cardiomyopathy underwent extended myectomy. In 45 cases, concomitant Cox-Maze IV procedure was performed; however, obstructive hypertrophic cardiomyopathy was the primary indication for surgery. Atrial fibrillation was paroxysmal in 26 patients (58%) and nonparoxysmal in 19 patients (42%). The mean age of patients was 52.8 ± 14.2 years (range, 22-74 years). Mean peak gradient was 90.7 ± 24.2 mm Hg, and interventricular septum thickness was 26.1 ± 4.3 mm. Mean atrial fibrillation duration was 17.3 ± 8.5 months. There were no early deaths. No procedure-related complications occurred with regard to ablation procedure. Complete atrioventricular block was achieved in 2 patients (4.0%). Mean crossclamping time was 61 ± 36 minutes. Peak left ventricular outflow tract gradient was 12.6 ± 5.5 mm Hg based on transesophageal echocardiography. The Maze IV procedure was used for ablation in all patients (radiofrequency ablation with bipolar clamp + cryolesion for mitral and tricuspid lines). Because of the atrial wall thickness (5-6 mm), applications were performed 8 to 10 times on each line. There were no cases of pacemaker implantation due to sinus node dysfunction. All patients were discharged in stable sinus rhythm. Mean follow-up was 23.7 ± 1.3 months. The rate of atrial fibrillation freedom was 100% (45 patients) at 6 months, 89% (40 patients) at 1 year, and 78% (35 patients) at 24 months. Concomitant ablation atrial fibrillation during septal myectomy in patients with obstructive hypertrophic cardiomyopathy is a safe and effective procedure and should be considered carefully in this patient group.