BACKGROUND: Previous studies have suggested truncal valve insufficiency may adversely affect outcome after common arterial trunk (CAT) repair. It is unknown if truncal insufficiency requiring truncal valve surgery (TVS) at the time of primary CAT repair impacts outcome. METHODS: Patients in The Society of Thoracic Surgeons Congenital Heart Surgery Database undergoing CAT repair from 2000 to 2009 were included. Outcomes were compared for patients with and without TVS at the time of CAT repair and were further stratified by interrupted aortic arch (IAA) repair. RESULTS: Of 572 patients (63 centers), median age at surgery was 12 days (interquartile range, 6 to 34). Twenty-three patients underwent concomitant TVS (n = 22 repair, n = 1 replacement) during CAT repair, and 4 patients underwent TVS later during the same hospitalization (n = 1 repair, n = 3 replacement). Thirty-nine patients underwent IAA repair at the time of CAT repair, 5 of whom had concomitant TVS. Mortality for CAT repair with TVS versus isolated CAT repair was 30% versus 10% (p = 0.0002). All 4 patients who required TVS later during the admission died. Truncal valve surgery was associated with increased mortality among CAT patients both with and without IAA repair, with the highest mortality (60%) among CAT patients undergoing IAA repair and TVS (n = 5). Common arterial trunk plus TVS had an increased risk of mechanical support and a longer hospital stay. CONCLUSIONS: Truncal valve surgery in patients undergoing CAT repair is associated with significant mortality. Repair of IAA and TVS at the time of CAT repair carries particularly high risk. Failure to address significant truncal insufficiency, necessitating early reoperation with TVS, had uniformly poor outcomes.