Summary of background data The curve pattern of idiopathic scoliosis is important for making decisions concerning bracing.However, whether the curve pattern changes during brace treatment have not been fully documented.The aim of this study was to investigate the changes of curve pattern during brace treatment in skeletally immature patients with adolescent idiopathic seoliosis (AIS).Methods From January 2002 to January 2011, AIS patients treated with a Boston or Milwaukee brace were recruited after meeting the following inclusion criteria: older than 10 years of age at initiation of bracing; having a Cobb angle of 25°-40°; with a Risser sign 0-2; being regularly followed until the weaning of brace or the necessity of surgical treatment; and without history of previous treatment.A total of 130 female and 11 male AIS patients were included.The mean age was 12.9 years at initiation of bracing, and the female patients were, on average, 2.7 months past menarche.The mean follow-up period was 2.6 years (range 1.0-5.5 years).The definitions of changes in curve patterns were divided into four categories as follows: (1) shift of the apex of the main curve; (2) change in the curve span of more than two vertebrae; (3) change in the main curve type with regard to the apex location; and (4) change of curve direction.The patients were divided into two groups.Group A was comprised of patients who had experienced one or more categories of curve pattern changes, and Group B was comprised of those who had not.Results Of these 39 patients, 14 had apex shifting, 2 underwent curve span changes, 22 experienced changes in the main curve type, and one female had both changes in the apex and curve span.At the initiation of bracing, patients in Group A demonstrated significantly lower menarchal status (P =0.018) and lower Risser grade (P =0.025) than those in Group B.The difference in the percentage of patients who underwent Boston bracing between the two groups was statistically significant (41.5 % for Group A vs.24.0 % for Group B, P =0.023).Conclusion Changes in curve pattern can occur during brace treatment.Patients with less skeletal maturity and those treated with a Boston brace are more susceptible to this phenomenon.