An ever-increasing number of patients with congenital heart disease are reaching adulthood; follow-up often requires right ventricular (RV) quantification. Complex anatomy, acoustic window, and active implants such as pacemakers may limit modalities, such as echocardiography and cardiac magnetic resonance imaging (MRI), in this population. Recent advances in multidetector row cardiac computed tomography (MDCT) allow multiphase, multislice reconstructions in any plane but have not been applied to RV quantification. Fourteen patients with tetralogy of Fallot or transposition of the great arteries underwent cardiac MRI and MDCT examinations, with comparable quantification of RV volumes and ejection fractions and no systematic error by Bland-Altman analysis using MRI as the gold standard.