This study aimed to determine the dimensions of the thoracic aorta and the predictors of aortic dimensions in girls and young women with Turner syndrome (TS). A cross-sectional study was performed at a secondary care center. The study compared 41 TS patients with 50 healthy age-matched control subjects. The mean age of the patients was 17 +/- 3.3 years. Magnetic resonance imaging was performed for all the patients. The thoracic aortic diameters of the patients were measured at nine positions. Adjustment for body surface area (BSA) was performed. The outcome for the patients was measured in terms of absolute and BSA-adjusted aortic dilation. In TS, both the absolute and the BSA-adjusted mean aortic diameters were smaller than or comparable with those of the control subjects. However, individual aortic dilation at one to four positions was found in four TS patients according to the uncorrected data and in five TS patients after BSA-adjustment. The aortic diameters correlated with height, weight, body mass index (BMI), and BSA at all positions (R = 0.34-0.60; all p < 0.04). The diameters of the aortic arch and the descending aorta correlated with a history of aortic coarctation (R = 0.35-0.52; p < 0.03). The presence of bicuspid aortic valves correlated at the descending part of the aorta (R = 0.38; p < 0.03). The mean thoracic aortic dimensions were not enlarged in girls or young TS patients. The BSA predicted aortic size at all positions. The prevalence of aortic dilation and aneurysm was lower in this population of girls and younger women with TS than in older TS populations.