Background: Data on outcomes of atrioventricular (AV) valve surgical procedures in patients with Fontan circulation are limited., Methods: We conducted a retrospective review of all children with Fontan circulation who underwent AV valve operations., Results: From 1981 to 2014, 581 patients underwent Fontan operations, and 9.3% (54/581) of them required AV valve operations. The first AV valve operation was performed before (n = 32), during (n = 15), or after (n = 7) the Fontan operation. The mean follow-up time was 9.8 ± 7.1 years (range, 6 months to 32 years). Operative mortality for the initial AV valve operation was 1.9% (1/54) and occurred in a patient who had the initial valve operation concomitantly with the Fontan. Late mortality was 5.7% (3/53). Heart transplantation was performed in 13.0% (7/54) of patients. Freedom from death or transplantation after the first AV valve operation was 89.8 ± 4.4% at 5 years (95% confidence interval [CI], 77.1 to 95.6) and 81.0 ± 6.2% at 10 years (95% CI, 65.0 to 90.2). Reoperation on the AV valve was performed in 44.4% (24/54) of patients. The median time to initial valve reoperation was 3.1 years (interquartile range, 0.8 to 7.4 years). Freedom from reoperation or transplantation was 63.4 ± 7.0% at 5 years (95% CI, 48.2 to 75.3) and 48.9 ± 7.9% at 10 years (95% CI, 32.8 to 63.2). Freedom from moderate or more regurgitation in patients who had not undergone reoperation or transplantation was 74.0 ± 6.9% (95% CI, 57.5 to 84.8) at 5 years and 67.5 ± 7.7% (95% CI:,50.0 to 80.0) at 10 years. After initial valve operation, thromboembolic events occurred in 13.0% (7/54) of patients, stroke occurred in 24.1% (13/54) of patients, pacemaker insertion was required in 16.7% (9/54) of patients, and protein-losing enteropathy was diagnosed in 7.4% (4/54) of patients. Of the 43 surviving transplant-free patients, 62.8% (27/43) were in New York Heart Association (NYHA) class I, 34.9% (15/43) were in NYHA class II, and 1 patient was in NYHA class III., Conclusions: The AV valve operation done before, during, or after the Fontan operation is associated with low operative mortality but a high reoperation rate with significant risk of late death, transplantation, and persistent AV valve regurgitation., (Copyright © 2015 The Society of Thoracic Surgeons. Published by Elsevier Inc. All rights reserved.)