BACKGROUND Systemic atrioventricular valve (morphologic tricuspid valve [TV]) regurgitation has been implicated in the development of systemic ventricular failure in congenitally corrected transposition of the great arteries (ccTGA), leading to timely referral for valve replacement. However, the surgical management of subpulmonary atrioventricular valve (morphologic mitral valve [MV]) regurgitation and outcomes has not been well studied. METHODS Of 108 ccTGA patients undergoing atrioventricular valve surgery from 1979 to 2022, 22 patients (20%) underwent MV surgery. Demographics, etiology of valve regurgitation, operative details, and outcomes of these 22 patients were retrospectively reviewed. Follow-up at 1, 5, and 10 years was available for 18 (82%), 13 (59%), and 11 patients (50%), respectively. RESULTS Median age was 37 years (interquartile range, 29-57 years). Intrinsic MV pathology was present in 18 individuals (82%). Operations included repair in 16 patients (73%), replacement in 6 (27%), and concomitant replacement of TV in 16 (73%). There was 1 perioperative death (5%) in a patient undergoing an emergent operation for severe acuteon-chronic heart failure due to worsening TV regurgitation. During a median follow-up of 12 years (interquartile range, 219 years), 7 patients (32%) died. Among the 16 patients who underwent repair, recurrent moderate or greater regurgitation was seen in 15%, 29%, and 43% of repairs in patients with annular, leaflet, and lead-induced regurgitation, respectively. CONCLUSIONS Concomitant TV and MV disease occur much less frequently than isolated TV disease in ccTGA. Intrinsic MV disease is most commonly observed but appears less amenable to successful repair compared with mitral repair in the systemic position and suggests MV replacement may be preferred in ccTGA patients. (Ann Thorac Surg 2024;117:560-7) (c) 2024 by The Society of Thoracic Surgeons. Published by Elsevier Inc.