False aneurysm formation of the great arteries after arterial switch operation. An infant with simple transposition of the great arteries underwent a two-staged arterial switch operation, after which mediastinal infection occurred. Continuous irrigation with povidone-iodine solution was performed for 10 days. After that, the patient experienced life-threatening hemorrhage three times. At the time of the second hemorrhage, greater omental transfer was performed. On postoperative day 109, false aneurysm was recognized, having developed from both great arteries. Successful repair was performed on postoperative day 110. 