Fixation with screws of Cotrel-Dubousset instrumentation was applied to replace the hooks in the treatment of scoliosis thoracic spine from 1987 by authors. The purpose of this study is to compare the result of treatment of the idiopathic scoliosis patient with pedicle screws and that with hooks and to clarify the advantages of pedicle screws in the treatment of idiopathic is scoliosis. The materials were 164 idiopathic scoliosis patients treated from 1987 to 1991 with average follow-up of 36 months(ranged 24 to 52 months). They were divided into three groups according to the fixation implants used. Forty-seven patients were treated with hooks only(hook group), 76 patients with screws and hooks(mixed group), and 41 patients with screws only(screw group). In the frontal curve correction, the hook group showed 49% of correction(preop. 59° to postop. 30°), the mixed group 60% of correction(preop. 58° to postop. 23°), and the screw group 63% of correction(preop. 51° to postop. 19°). For the patients with preoperative kyphosis less than 15°, there were significant improvement of sagittal curve in all groups from 3° to 19°. In the normokyphotic patients, there was no significant change. In rotational deformity, measured by Perdriolle method, the hook group 19% of correction, mixed group 20%, the screw group 24%. Hooks were dislodged in 17 cases and screws were found out of pedicle in 5 cases, but any neurologic complications or significant adverse effect on curve correction and loss of correction were not observed. Soft tissue infection was occurred in one patient, who was treated onservatively. In conclusion, screws fixation on the thoracic spine can be applied in the treatment of scoliosis without neurologic complications, and the screws provide rigid fixation and immediate stability after insertion with better correction in frontal, sagittal and less neurologic risk due to its extracanal placement and rigid fixation in derotation, and it makes the instrumental technique simpler, so the operation time shorter.