Non-operative treatment of idiopathic scoliosis is long and difficult. For the patient and the therapist it is particularly important to define early the therapeutic prognosis. The goal of this study is to verify if the initial reducibility at the beginning of treatment with the dynamic corrective brace (Spinecor) would be valid as a prognostic factor, allowing a more effective prognostic judgement of the final outcome treatment. This is a prospective study which includes 99 scoliosis patients (88 female, 11 male), with a mean age of new 12.6 years, treated by the dynamic corrective brace for progressive idiopathic scoliosis curves (29 degrees mean Cobb angle). The initial Cobb angle was compared to the pre-therapeutic Cobb angle. The results demonstrate that the reducibility of the scoliotic curves with the brace at the beginning of treatment provides a significant global prognostic index but is difficult to apply individually. Other factors should be considered, such as the impact of growth velocity on the spinal deformity at the onset of the adolescent growth spent as well as vertebral deformities diagnosed around the apex.