The contour of the azygoesophageal recess (AER) as seen with computed tomography (CT) is an important indicator of mediastinal disorders. Radiologists must recognize, however, that the AER contour varies with patient age. The configuration of the AER is dextroconvex in children younger than 6 years, nonconcave (ie, equally divided between convex and straight) in children aged 6-12 years, and concave (or adult-like) in adolescents and young adults (aged 12-20 years). The cause of this variation is not certain; however, chest wall configuration does not seem to be an important factor. Although a convex AER is normal and common in pediatric patients, this normal appearance must be distinguished from that of mediastinal abnormalities (eg, foregut malformation cysts, vascular anomalies, lymphadenopathy), which can also produce obvious or subtle convexity of the AER. An appreciation for the age-related variation in AER configuration helps in the interpretation of CT scans. Criteria such as attenuation, morphologic characteristics, cephalocaudal extent, and multicompartmental involvement may be helpful in the differential diagnosis, but, generally, mediastinal abnormalities that alter the AER are nonspecific in appearance.