The evaluation of vertebral rotation and torsion in idiopathic scoliosis is important both in treatment and prognosis. Standard radiography may be used to calculate only rotation but computerized tomography (CT) allows for an exact evaluation of both rotation and torsion. However, it is non feasible to use this method routinely. The purpose of this study is to compare the values obtained by CT scanning with those obtained on radiographic examination by the most commonly used methods of measuring rotation. We also evaluated the morphology of the vertebral canal and its relationship with the dural sac. Forty-seven idiopathic scoliotic curves were included in the study. The Perdriolle method of radiographic measurement of vertebral rotation is the one that most accurately reveals the true extent of the deformity. Vertebral torsion occurred early in 92% of the curves examined. Deformity of the vertebral canal was rarely observed, even in sever cases. The dural sac at the dorsal level was always shifted towards the concavity of the curve.