Background: The long-term outcome of repaired aortic coarctation may be complicated by dilatation of the ascending aorta notably in patients with bicuspid aortic valve. Magnetic resonance imaging was used to compare the size of the ascending aorta in patients with bicuspid or tricuspid aortic valve. Methods: In 50 patients with a repair of aortic coarctation, the size of the ascending aorta was measured in a bicuspid aortic valve group(n=11) and a tricuspid aortic valve group(n=39). The aortic diameter was measured at the level of the sinus of Valsalva and at the widest part of the ascending aorta using magnetic resonance imaging. Results: The mean age of patients at surgical repair was respectively 2.2±3.3 years for the bicuspid aortic valve group and 2.5±3.5 years for the tricuspid aortic valve group(p=NS) and the mean age at the time of the magnetic resonance imaging was 10.2±4.7 years and 9.3±5.9 years(p=NS) respectively. A significant difference in the aortic diameter was found between the bicuspid aortic valve group and the tricuspid aortic group both at the level of sinus of Valsalva(34.8±8.2 mm, 19.5±4.4 mm, respectively, p< 0.01) and at the level of the ascending aorta(36.8±7.2 mm, 16.9±3.4 mm, respectively, p< 0.01). Conclusions: The occurrence of ascending aortic dilatation is significantly associated with the presence of a bicuspid aortic valve. This requires long-term follow-up, which can be effectively performed by magnetic resonance imaging. Background: The long-term outcome of repaired aortic coarctation may be complicated by dilatation of the ascending aorta notably in patients with bicuspid aortic valve. Magnetic resonance imaging was used to compare the size of the ascending aorta in patients with bicuspid or tricuspid aortic valve. Methods: In 50 patients with a repair of aortic coarctation, the size of the ascending aorta was measured in a bicuspid aortic valve group (n = 11) and a tricuspid aortic valve group (n = 39). The aortic diameter was measured at the level of the sinus of Valsalva and at the widest part of the ascending aorta using magnetic resonance imaging. Results: The mean age of patients at surgical repair were respectively 2.2 ± 3.3 years for the bicuspid aortic valve group and 2.5 ± 3.5 years for the tricuspid aortic valve group (p = NS) and the mean age at the time of the magnetic resonance imaging were 10.2 ± 4.7 years and 9.3 ± 5.9 years (p = NS) respectively. A significant difference in the aortic diameter was foun d between the bicuspid aortic valve group and the tricuspid aortic group both at the level of the sinus of Valsalva (34.8 ± 8.2 mm, 19.5 ± 4.4 mm, respectively, p <0.01) and at the level of the ascending aorta (36.8 ± 7.2 mm , 16.9 ± 3.4 mm, respectively, p <0.01). Conclusions: The occurrence of ascending aortic dilatation is significantly associated with the presence of a bicuspid aortic valve. This requires long-term follow-up, which can be effectively performed by magnetic resonance imaging.