Objective: To test the hypothesis that immunotherapy prevents long-term disability in relapsing-remitting multiple sclerosis, we modelled disability outcomes in 14,717 patients. Methods: We studied patients from MSBase followed for ≥1 year, with ≥3 visits, ≥1 visit per year and exposed to a multiple sclerosis therapy, and a subset of patients with ≥15-year follow-up. Marginal structural models were used to compare the hazard of 12-month confirmed increase and decrease in disability, EDSS step 6 and the...