BackgroundMyositis is a rare disease associated with impaired health-related quality of life. A study evaluating the effectiveness of an intervention to improve the quality of life and well-being of myositis patients is presented.MethodsAll myositis patients in a health district were contacted. Thirty-four eligible patients were randomly assigned to the experimental (n = 17) or control (n = 17) group. A psychoeducational intervention of 5 100-min sessions focusing on the disease as related to daily life was conducted only in experimental patients. Several reliable tools to measure quality of life and well-being were administered twice, before and after the intervention, to both groups.ResultsIn the experimental group, post-test scores were higher than pre-test in quality of life, well-being, and self-efficacy to manage the disease. Improvements were more evident in the experimental group than controls in 70% of the variables studied. Specifically, sedentariness decreased and satisfaction with social relationships increased in the post-test evaluation to a greater degree in the experimental group than in controls.ConclusionsThis randomized controlled trial on a representative sample of myositis patients in an extensive population provides evidence indicating the effectiveness of a psychoeducational intervention for improving HRQoL, well-being, and self-efficacy to manage the disease.Trial registration: NCT06300983.