Objective: To evaluate the effect of Milwaukee brace treatment on adolescents with idiopathic scoliosis (AIS) with large curves (40° to 55°) who refuse to do surgery.Methods: In this retrospective cohort study, we gathered the clinical records of all adolescents with AIS with an initial curve of 40° to 55°. They had been referred to our center from December 1990 to January 2017. Although they had been advised to do surgery, they had all refused to do it. Their clinical data were recorded, such as sex, age, Risser sign, scoliosis, and kyphosis curve magnitude (at the beginning of brace treatment, weaning time, brace discontinuation, and minimum of 2 years after the treatment). Based on treatment success, the patients were divided into 2 groups: progressed and nonprogressed.Results: Sixty patients with an average initial Cobb angle of 44.93° ± 4.86° were included. The curve progressed in 57%, stabilized in 25%, and improved in 18% of the patients. In the progressed group (34 patients), 31 patients had undergone surgery. There was no significant association between the age of beginning the brace treatment and the final Cobb angle of nonprogressed group (p > 0.05). However, in-brace correction and initial Risser sign had a significant correlation with curve magnitude at the final follow-up (p < 0.05).Conclusion: Brace treatment seems to be effective in controlling the further curve progression in AIS with 40° and 55° curves. Our results can help physicians make sound decisions about the patients with larger curves who refuse to do surgery.