Purpose: To evaluate predictive factors for brace treatment outcome in adolescent idiopathic scoliosis (AIS) by a systematic review of the literature. Methods: Eligible studies evaluating one or more predictive factors for brace treatment outcome were included following a systematic search in PubMed and EMBASE on October 23, 2017. Inclusion criteria were: (1) subjects diagnosed with AIS, (2) age ≤ 18 years, (3) treated with a thoraco-lumbo-sacral orthosis (TLSO), and (4) evaluated one or more predictive factors of treatment outcome (failure and/or success). The methodological quality of included studies was independently assessed by two authors. Pooling was not possible due to heterogeneity in statistical analysis. Predictive factors were presented according to a best-evidence synthesis. Results: The literature search identified 26 studies that met the inclusion criteria, and multiple types of TLSO braces were identified (Boston, Wilmington, Chêneau, Osaka Medical College, Dresdner Scoliosis Orthosis and SPoRT). A total of 19 radiographic and 8 clinical predictive factors were reported. Strong evidence was found that lack of initial in-brace correction is associated with treatment failure. Moderate evidence suggests that brace wear time is associated with failure and success, whereas initial curve magnitude and curve type are not. Conclusion: The results of this review suggest that lack of initial in-brace correction is strongly associated with brace treatment failure. Future studies on the threshold for minimal immediate in-brace correction, as a potential indication for brace treatment, are recommended. Graphical abstract: These slides can be retrieved under Electronic Supplementary Material.[Figure not available: see fulltext.].