STUDY DESIGN : Systematic review of clinical studies. OBJECTIVES : To develop a pooled estimate of the prevalence of surgery after observation and after brace treatment in patients with adolescent idiopathic scoliosis (AIS). SUMMARY OF BACKGROUND DATA : Critical analysis of the studies evaluating bracing in AIS yields limited evidence concerning the effect of TLSOs on curve progression, rate of surgery, and the burden of suffering associated with AIS. Many patients choose bracing without an evidence-based estimate of their risk of surgery relative to no treatment. Therefore, such an estimate is needed to promote informed decision-making. METHODS : Multiple electronic databases were searched using the key words "adolescent idiopathic scoliosis," "observation," "orthotics," "surgery," and "bracing." The search was limited to the English language. Studies were included if observation or a TLSO was evaluated and if the sample closely matched the current indications for bracing (skeletal immaturity, age <15 years, Cobb angle between 20 degrees and 45 degrees ). One reviewer (L.A.D) selected the articles and abstracted the data, including research design, type of brace, minimum follow-up, and surgical rate. Additional data concerning inclusion criteria and risk factors for surgery included gender, Risser, age and Cobb angle at brace initiation, curve type, and dose (hours of recommended brace wear). RESULTS : Eighteen studies were included (observation = 3, bracing = 15). All were Level III or IV clinical series. Despite some uniformity in surgical indications, the surgical rates were extremely variable, ranging from 1 surgery of 72 patients (1%) to 51 of 120 patients (43%) after bracing, and from 2 surgeries of 15 patients (13%) to 18 of 47 patients (28%) after observation. When pooled, the bracing surgical rate was 23% compared with 22% in the observation group. Pooled estimates for surgical rate by type of brace, curve type, Cobb angle, Risser sign, and dose were also calculated. CONCLUSION : Comparing the pooled rates for these two interventions shows no clear advantage of either approach. Based on the evidence presented here, one cannot recommend one approach over the other to prevent the need for surgery in AIS. This recommendation carries a grade of D, indicating that the use of bracing relative to observation is supported by "troublingly inconsistent or inconclusive studies of any level." The decision to brace for AIS is often difficult for clinicians and families. An evidence-based estimate of the risk of surgery will provide additional information to use as they weigh the costs and benefits of bracing.