Analyses of aortic specimens obtained from patients with tetralogy of Fallot (TOF) revealed elastic fiber fragmentation. This study sought to determine the prevalence of aortic root dilation and aortic regurgitation (AR) in children after TOF repair and tested the hypothesis that aortic elastic properties are altered and related to aortic root dilation in these patients. Aortic dimensions, adjusted for body surface area and expressed as z scores, and AR were assessed echocardiographically in 67 children 8.3 ± 5.6 years after TOF repair. The aortic elastic properties were compared with those in 50 age-matched controls. The prevalence of aortic dilation (z score >2) was 88%, 87%, 61%, and 63% at the annulus, sinus of Valsalva, sinotubular junction, and ascending aorta, respectively. The z scores of the annulus (r = 0.41, p <0.001) and sinus (r = 0.33, p <0.01) were correlated with body surface area. Multivariate analysis identified the duration of follow-up after surgery as the only significant determinant of z scores of the annulus (β = 0.41, p = 0.001) and sinus (β = 0.33, p = 0.009). AR was present in 12% of patients who tended to have larger z scores at all aortic levels. Compared with controls, patients had significantly increased aortic stiffness (p <0.001) and reduced strain (p <0.001) and distensibility (p = 0.002). Aortic stiffness was correlated positively, whereas aortic strain and distensibility were correlated negatively, with the aortic root z scores at all levels. In conclusion, this study shows a high prevalence of aortic root dilation in children after the repair of TOF. Aortic stiffening occurred in these patients and may play a role in progressive aortic root dilation.