A clear understanding of the effectiveness of the thoracolumbosacral orthosis (TLSO) as a conservative treatment for idiopathic scoliosis is still necessary. In the past few years, the review of pertinent literature has emphasized the lack of properly matched control studies and erroneous interpretations of results due to the use of univariate analysis. Also, in a previous controlled study evaluating the bracing of idiopathic scoliosis, the researchers mixed different types of braces and patients. Therefore, their findings were not specific to any kind of orthosis. In our study, we responded to these criticisms by providing a homogeneous group of patients with a control group and by conducting a multivariate analysis to assess the effectiveness of the TLSO. All the patients at the University Pediatric Hospital Scoliosis Clinic aged 8 through 15 with initial Cobb's angle between 20 and 40° and evidence of progression were assessed. All the patients who used the TLSO and showed full compliance with treatment (n = 54) were compared with a control group. The control group consisted of the patients who needed the treatment with the brace but did not use it for several reasons (n = 47). Neither group showed significant differences in sex, initial age, initial Cobb's angle, menarche, Risser sign, or curve pattern. The mean follow-up period was 3.3 years after skeletal maturity. The results were analyzed using a multivariate analysis because the natural history of scoliosis is determined by multiple factors. The analysis showed that the control group had a threefold increase in the odds of ending with surgery compared to the treatment group (OR = 3.24, 95% CI, 1.09-9.60). The curve was more likely to progress >40° in the control group (OR = 2.83, 95% CI, 0.98-8.17).