Limited data are available on long-term outcome after repair of partial atrioventricular septal defects (pAVSD) in adults. We sought to review our experience. Between January 1, 1957 and December 31, 2016, 179 adult patients [median age (IQR) 34 (18, 72) years] underwent primary repair of pAVSD. The most common associated defects were secundum atrial septal defect (n = 38) and ventricular septal defect (VSD) (n = 7). Left atrioventricular valve (LAVV) zone of apposition (ZOA) was complete in 47 patients and LAVV regurgitation (≥moderate) was present in 73 patients. Autologous pericardium (n = 79, 45%) and polytetrafluoroethylene felt (n = 56, 32%) were mainly used for pAVSD closure. Repair techniques for LAVV regurgitation included: ZOA suture closure (n = 142), suture annuloplasty (n = 10) and posterior band annuloplasty (n = 9). Six had LAVV replacement. There were 61 deaths over a median follow-up of 21 years (IQR 10, 38), with only 4 early deaths. In a limited subset of patients with 80 paired measurements (n = 40), median right ventricular systolic pressure declined from 43 mm Hg (IQR 35-51) to 33 mm Hg (IQR 30-44) postoperatively (P < 0.001), and this improvement was sustained over long-term follow-up (P = 0.513). A total of 34 patients underwent a reoperation (recurrent LAVV regurgitation, n = 26; left ventricular outflow-tract obstruction, n = 7; LAVV stenosis, n = 4; patch dehiscence, n = 1) with cumulative incidence of 6% and 16% at 10 and 15 years, respectively. Repair of pAVSD in adults can be done safely with low early mortality and good long-term outcomes. Postrepair reduction of pulmonary artery pressure is significant. Despite the low re-operation rates, long-term surveillance remains essential.