This study is a retrospective review of 221 patients with untreated idiopathic thoracic and thoracolumbar scoliosis that were observed from the first months of life until maturity. There are three stages in the evolution of these curves: a single main period of progression, a secondary period of progression, and a stable period. The chronology of these different periods varies. In “infantile scoliosis,” the main period of accelerated increase of the curve occurs prior to 6 years of age. In “juvenile-puberal scoliosis,” it occurs from 6 years of age to the first stages of puberty, and in “puberal scoliosis,” the main increase occurs during puberty or adolescence. The prognosis of the scoliosis can be established at any age based on different parameters, such as the specific angle of rotation from birth to 6 years of age, the torsion angle from 6 years of age to P2, and the Cobb angle after puberty.