AIMS: Tricuspid regurgitation (TR) is related to heart failure (HF) progression in individuals with transposition of the great arteries (TGA) and a systemic right ventricle (sRV). While tricuspid valve (TV) variants have been described in the general population, their prevalence and impact in patients with congenital heart disease are still unknown. We aim to systematically describe TV morphology in patients with TGA and sRV and identify factors associated to more than mild regurgitation using transthoracic 3D echocardiography. METHODS AND RESULTS: Echocardiographic exams of adults (>18years) with a sRV, including TGA following Mustard/Senning repair and congenitally corrected TGA (ccTGA) followed at a single tertiary center were retrospectively reviewed by two independent observers. A dedicated software for tricuspid annulus (TA) measurements from 3D images was used. Among 85 patients with a sRV, TV anatomy assessment by 3D echo was feasible in 74 (87%, 41 ± 12 years, 35% female, 49% ccTGA): non-trileaflet morphology was demonstrated in 54% of ccTGA and in 42% of TGA patients. Bicuspid and pentacuspid TV were more frequent in TGA, while quadricuspid TV was the second most frequent TV morphology in ccTGA patients. Interobserver agreement for TV morphology, prolapse, tenting height and annular size was good. By logistic regression, age, sex, presence of one prolapsing leaflet and most 3D measurements of TA from the dedicated software were associated with TR severity, while TV anatomy was not. On multivariable analysis, sex, prolapsing leaflets (OR 20.2, 95% CI: 4.62-127.7; p = 0.002), TA area by 3D (OR 1.3, 95% CI:1.02-1.79; p = 0.04) and maximum leaflets tenting height (OR 31, 95% CI: 2.8-170; p = 0.02) retained significant association to moderate/severe TR. CONCLUSIONS: Assessment of TV morphology by 3D transthoracic echocardiography is feasible and reliable in TGA patients with sRV. In our cohort, some variants were more common than previously described prevalence in the general population. While non-trileaflet morphology is frequent, significant TR is mainly associated with annular dilation, leaflet tenting, and prolapse rather than valve anatomy alone. Further studies are required to investigate the clinical relevance of TV anatomical variants in this subset.