Background: Atrial fibrillation (AF) is common among adult patients with atrial septal defects (ASDs). Catheter ablation or Maze procedure can be considered for AF before or concurrently with closure of ASD. However, the fate of preoperative AF is not well established. This study examined the postoperative course of patients who had AF before undergoing ASD correction. Methods: A total of 471 patients (131 men, 42.4 짹 14.2 years) underwent transcatheter closure (n = 237, 50%) or surgical repair (n = 234, 50%) of ASD. Preoperative AF was documented by electrocardiogram or Holter monitoring. Postoperative AF was confirmed by electrocardiogram or Holter monitoring taken every 3 and 12 months, respectively. Results: Forty patients had AF before transcatheter closure (n = 10) or surgical repair (n = 30) of ASD. Compared to those without preoperative AF, patients with AF were older, and had larger left atrial size. During the follow-up period of 44 짹 28 months, excluding 15 patients who had undergone surgical repair with a concurrent Maze procedure, sinus rhythm was maintained in seven (88%) of eight patients with paroxysmal AF. However, only three (18%) of 17 patients with persistent AF maintained sinus rhythm. Among 15 patients treated with Maze procedure, 12 (80%) patients maintained sinus rhythm. Conclusions: Hemodynamic correction of ASD was effective in converting to sinus rhythm in most patients with preoperative paroxysmal AF. Therefore, concurrent Maze procedure or transcatheter ablation before ASD correction should be considered only in patients with persistent AF.