One CT-scan at the central part of the vertebral body of the apical vertebra of 32 patients with right convex thoracic idiopathic scoliosis and one CT-scan of either T8 or T9 of 22 normal subjects are included in this study. The position of the aorta in relation to the apical vertebra of the scoliotic patients and the corresponding vertebra of the normal subjects was determined at the horizontal plane. The mean lateral translation of the aorta in relation to the mid axis of the vertebral body increased from 19.7 +/- 4.3 mm in the normal group to 26.4 +/- 4.1 mm in the scoliotic group (p = 0.0001). In the normal group the aorta was located 41.7 +/- 8.6 mm in front of a perpendicular line to the mid axis of the vertebral body and in the scoliotic group this distance was reduced to 30.0 +/- 9.0 mm making the position of the aorta more posterior in the scoliotic group (p = 0.0001). This was in accordance with a decreased mean kyphosis-lordosis index from 0.53 +/- 0.06 in the normal group to 0.46 +/- 0.07 in the scoliotic group (p = 0.01). The position of the aorta, also expressed as the angle formed between the aorta and the vertebral body, the "aorto-vertebral angle", was increased from 24.4 degrees +/- 6.9 degrees in the normal group to 41.4 degrees +/- 8.4 degrees the scoliotic patients, (p = 0.0001). The aorto-vertebral angle did not change significantly with increasing Cobb angle (p = 0.26) but was positively correlated to the vertebral rotation (p = 0.0001). An estimation of the length of the intercostal arteries revealed a significantly greater R (right)/L (left) index in the scoliotic patients 1.18 +/- 0.11 than in the normal subjects 1.08 +/- 0.06 (p = 0.0003). It is concluded that the rotation and the anterior displacement of the vertebral body in scoliosis result in a deviation of the aorta along the left (concave) side of the vertebral body to a more posterior position relative to the vertebral body with a possible increased length of the intercostal artery on the right (convex) side.