A Core Outcome Set (COS) for treatment of adolescent idiopathic scoliosis (AIS) is essential to ensure that the most meaningful outcomes are evaluated and used consistently. Measuring the same outcomes ensures evidence from clinical trials and routine clinical practice of different treatments can be more easily compared and combined, therefore increasing the quality of the evidence base. The SPINE-COS-AYA project aims to develop a gold standard COS which can be used internationally in research and routine clinical practice to evaluate the treatment (surgical and bracing) of AIS. In this qualitative study, the views of adolescents and young adults with AIS (10-25 years of age), their family members and healthcare professionals in a UK region were sought, via interviews, on treatment outcomes. Participants were purposively recruited from a variety of sources including NHS outpatient clinics and social media. Semi-structured interviews were analysed using thematic analysis. Key findings will be presented, to include potential core outcome domains identified by the different subgroups. The core outcome domains identified in this research programme will subsequently form part of an international consensus survey to agree a COS. In future, if the COS is used by healthcare staff and researchers, it will be easier for everyone, including patients and their families, to assess which treatment works best.