Purpose: Describe the change in self-efficacy after a supported osteoarthritis self-management program.Materials and methods: An observational register-based study comprising 11 906 patients. Participants with hip or knee osteoarthritis self-reported at baseline, 3 and 12 months. Self-efficacy for pain and other symptoms were assessed with the Arthritis Self-efficacy Scale. Change was analyzed using a mixed-effect model for repeated measurements.Results: In total, 9440 (pain subscale) and 9361 (symptom subscale) patients reported self-efficacy scores at baseline and at least one follow-up. The lowest self-efficacy at baseline was reported by patients with low education, walking difficulties, comorbidity and low physical activity level. Overall, the self-efficacy scores improved at the 3-month follow-up and returned to baseline at the 12-month follow-up. Younger age (pain and symptom subscales) and exercise (pain subscale) were associated with a greater increase in self-efficacy. Obesity (pain subscale) and hip problems (pain and symptom subscales) were associated with lower self-efficacy at baseline and a greater decrease at follow-up.Conclusion: Self-efficacy was related to the level of education, physical activity, mobility, and comorbidity. In addition, hip problems or obesity were associated with greater difficulties in enhancing or maintaining self-efficacy. An increased focus on patients with hip problems or obesity might help to improve outcomes after supported self-management programs for osteoarthritis.IMPLICATIONS FOR REHABILITATIONSelf-efficacy increased more in younger patients and in those who opted for exercise as part of the intervention, which indicates that offering supported self-management early in the course of the disease might be important.Lower self-efficacy at baseline and reduced beliefs about their ability to manage pain indicate that patients with hip OA or obesity may need to be given a special focus by healthcare.Self-efficacy in managing pain and other symptoms seemed to increase after a supported self-management osteoarthritis program, but was not maintained at the 12-month follow-up, indicating that more on-going support might be needed to maintain self-efficacy.