The results of surgical closure of atrial septal defect of secundum type (ASD) in 28 patients over 40 years of age with a closed method, circumclusion ad modum Søndergaard, are presented. One death occurred in the postoperative period caused by cerebral embolism in a patient with increased pressure in the pulmonary artery and atrial fibrillation. The most frequent postoperative complications were transient atrial arrhythmias and the post-pericardiotomy syndrome. The pressures in the pulmonary artery decreased in all patients, who had increased pressures pre-operatively. In two patients with pulmonary vascular resistance of 6 mmHg/l/min before operation the resistance was significantly reduced postoperatively. Residual shunts of less than 30% of the systemic flow were present in 4 cases. The ASD recurred years after the operation in two patients. At follow-up examinations on an average 44 months after operation, 75% had improved. In 20 cases the heart was reduced in size. In the remaining 6 the heart size was unchanged or larger, in spite of eliminated shunts in 5 of the 6 patients. Of 8 patients with atrial fibrillation before operation, two gained stable sinus rhythm postoperatively. It is concluded that circumclusion is also an effective method in the elderly patient with ASD and that such patients should undergo surgical repair of the defect.