Key PointsQuestionWhat is the effect of an artificial intelligence–based smartphone app vs usual care alone or web-based self-management support on musculoskeletal health in patients with neck and/or low back pain referred to specialist care?FindingsIn this randomized clinical trial of 294 adults with neck and/or low back pain referred to specialist care, the individually tailored app adjunct to usual care did not significantly improve musculoskeletal health more than usual care alone or nontailored web-based support at 3 months.MeaningThese findings suggest that further research is needed to investigate the utility of implementing digitally supported self-management interventions for those with neck and/or low back pain referred to specialist care and to identify instruments that capture changes in self-management behavior.