Objectives: Studies evaluating the long-term outcome of adults with ventricular septal defect (VSD) are important to inform patients about prognosis. This study investigated the long-term outcome of patients with perimembranous VSD (pmVSD) followed in the Belgian Registry on Adult Congenital Heart Disease. Methods: All pmVSD patients in the registry were analyzed. Results: Two hundred and sixty-six patients were studied. Fifteen patients had Eisenmenger syndrome. One hundred and seventy-three had isolated pmVSD and 78 had pmVSD with concomitant lesions. Of the patients with isolated pmVSD, 52% were male, median age was 29 years (IQR 24-35 years) and median follow-up duration was 18 years (IQR 10-25 years). Fifty-three (31%) patients underwent VSD closure and 10 (19%) had a residual shunt. Most (93%) patients were in NYHA class I. No patients died. Two (4%) patients developed atrial arrhythmia and 2 (4%) required pacemaker implantation. Seven (14%) developed left ventricular outflow tract obstruction (LVOTO). In the unrepaired pmVSD group, 4 developed endocarditis. In the entire group, moderate or severe aortic regurgitation (AR) occurred in 9 (5%) patients. Conclusions: Long-term survival in patients with isolated pmVSD was not uneventful. Moderate or severe AR might develop and endocarditis occurred in patients without VSD repair. Complications after VSD closure included atrial arrhythmia, pacemaker implantation and LVOTO