Background: Outcomes after atrioventricular (AV) valve operations in patients with functional single ventricles are unclear. Methods: From 1988 to 2010, 76 consecutive patients with single ventricles underwent AV valve operations for regurgitation at a single institution. Five replacements, 66 repairs, and 5 valve closures were performed at a median age of 1 year (range, 1 day-14 years) on 43 tricuspid, 9 mitral, and 24 common AV valves. Results: Hospital mortality was 17% (13/76). The follow-up was 100% complete. There were 15 late deaths. There were 48 survivors with a mean follow-up of 8.3 ± 6 years. One- and 10-year Kaplan-Meier survival after AV valve operations was 72% (95% confidence interval [CI], 60%-81%) and 61% (95% CI, 48%-71%), respectively. Independent predictors of overall mortality were presence of a common AV valve (p = 0.03), requirement for postoperative mechanical circulatory support (p = 0.02), and timing of valve operations between initial palliation and performance of a bidirectional cavopulmonary shunt (BCPS) (p = 0.047). Ten-year freedom from valve reoperation and from thromboembolic events of hospital survivors was 56% (95% CI, 38%-70%) and 70% (95% CI, 56%-80%), respectively. At last follow-up, 11 of 48 surviving patients (23%) had moderate to severe regurgitation, and pacemaker implantation was required in 6 patients. Only 34 patients reached the stage of Fontan completion. Conclusions: AV valve regurgitation is a considerable burden for the patient with a single ventricle, especially when appearing at a young age. A quarter of patients died within the first year after operation, and they had considerable morbidity in terms of reoperation, thromboembolic events, and pacemaker implantation. Their chances of reaching Fontan completion seemed decreased.