Aortic dilation at the level of the aortic root can be caused by a variety of congenital or acquired conditions that lead to weakening of the aortic wall. In this retrospective study, we sought to determine the frequency of different associated diagnoses from children with aortic dilation seen at a single institution. A total of 377 children (68 % male) met study inclusion criteria. Patients were classified based on the suspected or confirmed associated diagnosis in one of the following categories: congenital heart disease (241/377, 64 %), chromosomal (34/377, 9 %), Marfan syndrome (26/377, 7 %), other genetic and non-genetic (22/377, 6 %), Loeys-Dietz syndrome (6/377, 2 %), and unknown (48/377, 13 %). Bicuspid aortic valve was by far the most prevalent congenital heart defect (206/241, 85 %), while Turner syndrome was the most frequent chromosomal abnormality (12/34, 35 %). Patients with Marfan syndrome were more likely to have severe dilation of the ascending aorta (p = 0.002) and to require aortic root replacement surgery (p < 0.001) compared to those in other diagnosis categories. Conclusion: The differential diagnosis of aortic dilation is broad and requires a careful assessment of cardiac anatomy. Evaluation by a clinical geneticist in this setting should be strongly considered given the high frequency of associated genetic conditions.What is Known:• Aortic dilation is frequent in bicuspid aortic valve and other congenital heart defects.• Aortic dilation can be seen in several connective tissue disorders. Limited information is available in regard to the differential diagnosis of aortic dilation in children.What is New:• In patients with aortic dilation concurrent congenital heart disease is frequently diagnosed.• Almost 18 % of cases in the present study had a defined presumptive or confirmed genetic diagnosis. We suggest considering a genetics evaluation in the setting of aortic dilation.