Background: To compare the accuracy of cardiac magnetic resonance (CMR) evaluation of aortic annulus (AoA) versus multidetector computed tomography (MDCT) in patients referred for transaortic valve implantation (TAVI). Methods: 50 patients were studied with a 1.5-T scanner (Discovery MR450, GE Healthcare, Milwaukee, WI). Steady-state free precession cine acquisitions were acquired to reach two long-axis view of the aortic root and ascending aorta. Thus, serial short-axis cines orthogonal to the AoA (3-mm thickness with 1.5-mm overlapping) were imaged. The following parameters were assessed with CMR and compared with those obtained with MDCT: AoA maximum diameter (AoA-Dmax), minimum diameter (AoADmin), and area (AoA-A), length of the left coronary, right coronary, and non-coronary aortic leaflets, degree (grades 1 to 4) of aortic leaflet calcification and distance between AoA and coronary artery ostia. Results: AoA-Dmax, AoA-Dmin and AoA-A were 26.45±2.83 mm, 20.17±2.20 mm, 444.88±84.61 mm2 and 26.45±2.76 mm, 20.59±2.35 mm and 449.78±86.22 mm2 bv MDCT and CMR. respectivelv. The length of left coronary, right coronary, and non-coronary leaflets were 14.02±2.27 mm, 13.33±2.33 mm, 13.39±1.97 mm, and 13.95±2.18 mm, 13.30±2.14 mm, 13.46±1.80 mm by MDCT and CMR, respectively, while the scores of aortic leaflet calcifications were 3.4.±0.7 vs. 2.97±0.77. Finally, the distance between AoA and left main and right coronary artery ostia was 16.21±3.07 mm, 16.02±4.29 mm and 16.14±2.83 mm, 16.14±4.36 mm by MDCT and CMR, respectively. With regard to AoA-Dmax (r: 0.96, p<0.001), AoA-Dmin (r: 0.91, p<0.001) and AoA-A (r: 0.97, p<0.001), the Pearson's correlation showed good agreement between MDCT and CMR with mean differences of 0±0.79 mm, -0.43±0.99 mm and -4.90±21.19 mm2 at Bland-Altman analysis, respectively. Similarly, Pearson's correlation showed good agreement between MDCT and CMR for the left coronary (r: 0.97, p<0.001), right coronary (r: 0.95, p<0.001) and non-coronary (r: 0.95, p<0.001) aortic leaflets with mean differences of 0.07.0±0.46 mm, 0.02±0.74 mm and -0.07±0.60 mm2 at Bland-Altman analysis, respectively. No difference was observed between MDCT and CMR regarding the distance between AoA and the left main coronary artery ostium (r: 0.93, p<0.001; mean difference: 0.07±1.09 mm) and between AoA and the right coronary artery ostium (r: 0.97, p<0.001; mean difference: -0.11±1.06 mm). Finally, CMR underestimated aortic leaflet calcification score as compared to MDCT. Conclusions: AoA assessment with CMR is accurate. CMR may be a valid imaging alternative in patients unsuitable for MDCT.