BACKGROUND: Current treatments for relapsing remitting multiple sclerosis (RRMS) reduce inflammation, but have a partial or modest effect on disability. This effect may require a much longer follow-up than standard trial design, in particular in RRMS with relatively-preserved functional reserve. We aimed to assess the long-term clinical evolution of RRMS patients exposed to atorvastatin in two trials (ACTIVE and ARIANNA). METHODS: We retrospectively looked at 69 participants randomized with atorvastatin or placebo as add-on therapy to interferon-beta for 24 months at a single MS centre. We recorded relapses, 1-point EDSS progression and progression to EDSS 4.0. Cox regression was performed for these three questions. A Poisson regression model was used to evaluate the association between atorvastatin treatment and annualized relapse rate (ARR). RESULTS: After 8.4 ± 2.3 (3.7-11.9) years from trial, the use of atorvastatin was associated with reduced risk of 1-point EDSS progression (HR = 0.440; 95%CI = 0.225-0.861; p = 0.017), and of EDSS 4.0 (HR = 0.310; 95%CI = 0.123-0.784; p = 0.013). We found no significant association between atorvastatin and relapses. DISCUSSION: These data suggest that a delayed treatment effect may be seen with atorvastatin added to interferon-beta, eight years after entering the clinical trials. Long-term follow-up of trial cohorts should be mandated.