Objective: Turner syndrome (TS) is a rare disorder affecting 1/2500 female newborn. Aortic dilatation (AD) and aortic dissection represent a major concern in TS. The aims of our study were to describe the aortic root growth, potential aortic dilatation (AD) risk factors and cardiovascular outcomes in a cohort of patients with TS. Methods: Among 204 adult patients included, 197 were studied using a standardized 1.5 Tesla MRI protocol. AD was defined as an aortic diameter ≥20 mm/m2 at the Valsalva sinuses and/or at the ascending aorta, when indexed to body surface area. Results: At baseline, AD was present in 81/197 (41.1%) and 32/197 (16.2%) of patients, at the levels of Valsalva and ascending aorta, respectively. The aortic Valsalva diameter was larger in patients treated for thyroiditis (P < 0.001). Potential risk factors of AD were aging (P < 0.001) and the presence of bicuspid aortic valve (BAV) (P = 0.002). The hazard ratio (HR) of AD occurrence in the presence of BAV was 2.2 (95% CI: 1.33–3.71). After a median follow-up period of 5.1 years (n = 143), AD was present in 58/143 (40.6%) and 25/143 (17.5%) of patients at the levels of Valsalva and ascending aorta, respectively. The median aortic growth of the Valsalva sinuses remained stable. At the ascending aorta, it increased by 0.14 ± 0.61 mm/year. Only one aortic-related death was observed. Conclusion: AD is common in adult patients with TS. However, our results are rather reassuring, as the median aortic diameters remained stable after 5.1 years and few aortic events were observed.