This study intends to provide a detailed overview of the types and rates of peri-operative complications after surgical correction of an isolated ASD II. The transvenous approach to the occlusion of atrial septal defects has yielded promising results during its first 5 years of clinical trials, but before it can be established as a routine measure, definite proof is needed to demonstrate that its rate of serious complications does at least not exceed that of the surgical closure. Between 1985 and 1992, 232 consecutive patients underwent surgical closure of a secundum atrial septal defect. Among the patients 118 were children (<18 years; 79 girls and 39 boys) with a mean age of 8.9± 5 2 years (4 months-17 years) and 114 adults (74 women and 40 men) with a mean age of 28.5 ±10.8 years (18–69 years). Pre-operatively eight children (6.8%) and eight adults (7%) were treated for right heart failure. Mean pulmonary artery pressure was 20.4 ± 10.4 mmHg for the children and 19.3 ±7 mmHg for the adults. The average pulmonary artery to systemic flow ratios were 2.9:1 and 3:1 for children and adults, respectively. Thirty children (25.4%) and 15 adults (13.2%) underwent patch closure while direct suture was the method used for the remaining patients. Average cardiopulmonary bypass time was 35.7 /'b1 17.9 min for the children and 41.5± 19.9 min for the adults. The length of the procedure (skin to skin) was a mean of 116 min in the young group, and 141 min in the adult group. One adult patient died during his hospital stay as a consequence of sepsis (0.4% total mortality rate). Severe early complications (pericardial tamponade, renal failure, sepsis) occurred in three children (2.5%) and ten adults (8.8%), moderately severe complications (pneumonia, pleural effusion requiring thoracocenthesis) in four children (3.4%) and seven adults (6.1%) and mild complications (atelectasis, gastrointestinal, urinary tract infection, pleural effusion) in 86 children (72.9%) and 77 adults (67.5%). Only 25 children (21.2%) and 20 adults (17.5%) experienced an uneventful peri-operative period. The results show that an isolated secundum atrial septal defect can be surgically closed with a minimal mortality but significant complications can occur. The majority of the early complications for the patients were of minor significance, and severe complications were observed more often in adults than in children.