Purpose Adolescent idiopathic scoliosis (AIS) is characterized by coronal scoliosis and often a sagittal hypokyphosis. The effect of bracing on the sagittal profile is not well understood. The aim of this study is to assess the effect of night-time bracing on the sagittal profile in patients with AIS. Methods We retrospectively included AIS patients with a main curve of 25–45° treated with a night-time brace in our institution between 2005 and 2018. Patients with estimated growth potential based on either Risser stage, hand X-rays, or menarchal status were included. Coronal and sagittal radiographic parameters were recorded at both brace- initiation and -termination. Patients were followed until surgery or one year after brace termination. Results were compared to a published cohort of full-time braced patients. Results One hundred forty-six patients were included. Maximum thoracic kyphosis (TK) increased 2.5° (± 9.7) ( p  = 0.003), corresponding to a 3.5-fold relative risk increase post bracing in TK compared to a full-time brace cohort. Twenty-seven percent ( n  = 36) of the patients were hypokyphotic (T4/T12 < 20°) at brace initiation compared with 19% ( n  = 26) at brace termination ( p  = 0.134). All other sagittal parameters remained the same at follow-up. We found no association between progression in the coronal plane and change in sagittal parameters. Conclusion This is the first study to indicate that night-time bracing of AIS does not induce hypokyphosis. We found a small increase in TK, with a substantially lower risk of developing flat back deformity compared to full-time bracing. The coronal curve progression was not coupled to a change in TK.