The benefits of surgical closure have been unclear for adult atrial septal defect (ASD) with severe pulmonary hypertension (PHT). We tried to evaluate improvement of PHT and long-term survival after surgical closure comparing with medical follow-up. Methods: From 1996 to 2006, we included a total of 71 adult ASD patients (age; 43짹15 yrs) with severe PHT documented by echocardiography. Inclusion criteria were ASD diameter > 15 mm, enlarged right ventricle, and baseline peak velocity of tricuspid regurgitation (TR) > 4.0 m/sec. We excluded 5 patients with Eisenmenger syndrome documented by cardiac catheterization. Surgical closure was performed on 55 patients (OP group) and the remaining 16 patients were followed up medically (MED group). Improvement of PHT was defined as TR velocity < 3.5 m/sec on follow-up echo. Results: There were no significant differences in terms of gender(% of male, MED vs OP; 25% vs 18%), ASD diameter (31짹18 mm vs 31짹8 mm), cardiac rhythm (% of atrial fibrillation, 31% vs 16%), and TR velocity (4.5짹0.7 m/sec vs 4.5짹0.4 m/sec) between two groups, but the MED group was significantly older (57짹14 yrs vs 39짹14 yrs, p<0.001). During the follow-up of 46짹33 months, there were 5 (31%) deaths in the MED group, while no operative or late death in the OP group (p<0.001), and the 5-year actuarial survival rate of the OP group was significantly higher than the MED group (58짹15%, p<0.05). On subgroup analysis according to age, the OP group showed significantly better survival rate than the MED group (p<0.05) in elderly patients (age > 50 yrs). In the OP group, TR velocity was significantly decreased from 4.5짹0.4 to 3.0짹0.7 m/sec on follow-up echo (vs 4.5짹0.4 to 4.9짹0.5 m/sec, p<0.001), and improvement of PHT was observed in 47 (85%) patients (vs 0 (0%), p<0.001). On multivariate analysis, female gender and lower baseline TR velocity were the significant independent predictors of improved PHT after surgery. Conclusions: In adult ASD with severe PHT, surgical closure can be safely performed and improve PHT effectively. Especially in elderly patients, ASD closure is significantly related with better survival rate.