Background and purpose - Routine outcome measurement has been shown to improve performance in several fields of healthcare. National spine surgery registries have been initiated in 5 Nordic countries. However, there is no agreement on which outcomes are essential to measure for adolescent and young adult patients with a spinal deformity. The aim of this study was to develop a core outcome set (COS) that will facilitate benchmarking within and between the 5 countries of the Nordic Spinal Deformity Society (NSDS) and other registries worldwide. Material and methods - From August 2015 to September 2016, 7 representatives (panelists) of the national spinal surgery registries from each of the NSDS countries participated in a modified Delphi study. With a systematic literature review as a basis and the International Classification of Functioning, Disability and Health framework as guidance, 4 consensus rounds were held. Consensus was defined as agreement between at least 5 of the 7 representatives. Data were analyzed qualitatively and quantitatively. Results - Consensus was reached on the inclusion of 13 core outcome domains: "satisfaction with overall outcome of surgery", "satisfaction with cosmetic result of surgery", "pain interference", physical functioning", "health-related quality of life", "recreation and leisure", "pulmonary fatigue", "change in deformity", "self-image", "pain intensity", "physical function", "complications", and "re-operation". Panelists agreed that the SRS-22r, EQ-5D, and a pulmonary fatigue questionnaire (yet to be developed) are the most appropriate set of patient-reported measurement instruments that cover these outcome domains. Interpretation - We have identified a COS for a large subgroup of spinal deformity patients for implementation and validation in the NSDS countries. This is the first study to further develop a COS in a global perspective.