Normal thoracic aortic dimensions in adults have been established by means of computed tomography (CT), but such measurements are not available in children. To establish normal standards, contrast material-enhanced chest CT scans of 117 children and adolescents, ranging in age from 2 weeks to 19 years, were reviewed retrospectively. Patients with congenital heart disease, vascular anomalies, renal disease, hypertension, and connective-tissue disorders were excluded, resulting in 97 studies. Diameters of the thoracic aortas were measured at three levels. Interobserver and intraobserver variances were determined. A direct linear relationship to patient age was observed, and regression analysis was performed. These standards help in differentiating the normal from the abnormal aorta on chest CT scans of children.