Background: Atrial septal defect (ASD) is the most common congenital cardiac anomaly, accounting for 30 percent of congenital heart disease detected in the adult. Many patients with ASD are well tolerated and reach adult without significant symptoms. The patients with ASD die 4th and 5th decades, but prolonged survival is not uncommon. In general, the survival depends on whether pulmonary hypertension develops during adulthood or not. The most common cause of death in the patients with ASD is right ventricular failure or arrhythmias. Materials and methods: From January 1988 to June 1997, 33 cases of ASD underwent open heart surgeries in our hospital. Among them, 31 cases were adult ASD, and 2 tricuspid regurgitation, 1 pulmonic stenosis, 1 mitral regurgitation, 1 tricuspid regurgitation, and 1 coronary artery disease were combinded. All of the patients underwent surgical repair using autologus pericardial patch or direct closure. Results: The postoperative course was smooth and uneventful. Most of the patients showed significant improvement in ECG finding, hemodynamic profile, radiologic finding, and echocardiography, after surgery. Conclusions: Conclusively, most of the ASD should be closed even in patients over the age of 60 years, and early surgical repair must be done to prevent pulmonary hypertension, right ventricular failure, and arrythmias.