The high mortality rate from aortic dissection of women with Turner syndrome (TS) achieving ovum donation pregnancies has highlighted the need for a refinement of cardiac screening protocols. Echocardiography and magnetic resonance imaging (MRI) are used to assess the risk factors, aortic root dilatation, bicuspid aortic valve, and coarctation, but the relative merits of each modality are unclear. Cardiovascular screening was performed in 128 unselected women with TS (mean age +/- SD, 31.1 +/- 8.5 yr) using echocardiography (n = 120) and MRI (n = 115) and in 36 age-matched normal control women. Clinical history, anthropometric measurements, blood pressure, and metabolic parameters were recorded. Echocardiography was normal in 53% of women with TS; MRI was normal in 34%. Aortic root dilatation was identified in 16% of women by echocardiography, 33% on MRI criteria, and 7% by both modalities. Height-adjusted echocardiographic aortic root dimensions were greater in TS than controls (2.90 vs. 2.62 cm; P = 0.010). Bicuspid aortic valve and increasing age were associated with greater aortic dimensions; the latter effect was more marked in TS than controls. On MRI, ascending aortic diameter was greater in TS than control women (2.83 vs. 2.52 cm; P = 0.029), but descending aortic diameter and ascending/descending aortic ratio were not, because these may be affected by the presence of coarctation. The two techniques are complementary and identify different aspects of cardiovascular pathology. Ascending/descending ratio on MRI circumvents issues of stature, but may be influenced by descending aortic abnormalities. We present reference ranges for absolute aortic dimensions in a TS population to aid future interpretation of these measurements.