A retrospective study was conducted on 67 patients affected by thoracolumbar and lumbar adolescent idiopathic scoliotic curves treated by a TLSO orthosis of new design (Progressive Action Short Brace: P.A.S.B.). The variation relative to Cobb angle, apical vertebra rotation and mean rotation of all vertebrae included in the curve was statistically analysed with ANOVA test for repeated measures from the start of treatment to follow-up (mean follow-up 36.37±11.71 SD months). Curve correction was obtained in 41 (61.2%) out of the 67 patients (curve correction) and curve stabilisation in 23 patients (34.3%). Progression occurred in 3 patients (4.5%). Results were statistically significant (P < 0.001).