Background: To evaluate efficacy and safety of fingolimod for relapsing-remitting multiple sclerosis, particularly in patients previously exposed to natalizumab. Method: Prospective observational single-centre second-line cohort study. Results: Among 71 patients treated with fingolimod 0.5 mg/day for a mean duration of 21.75 ± 12.60 months, the annualized relapse rate was 0.66 (C.I. 95% 0.27-1.05) with a significant difference between 26 patients with prior natalizumab exposure (1.15; C.I. 95% 0.12-2.17) and 45 not exposed (0.38; C.I. 95% 0.18-0.57; p = 0.002). In a multivariate negative regression model, only previous exposure to natalizumab (p = 0.049) and duration of fingolimod treatment (p < 0.001) significantly correlated with the annualized relapse rate. Previous exposure to natalizumab (p = 0.028) and duration of treatment with fingolimod (p < 0.001) were confirmed by restricting the analysis to the first 12 months of treatment with fingolimod, but were no longer statistically significant by analysing only patients (n = 51) with at least 12 months of treatment with fingolimod (0.32; C.I. 95% 0.08-0.55 vs. 0.22; C.I. 95% 0.11-0.32; p = NS). No differences were observed in neuroradiological outcomes and disability progression in patients exposed to natalizumab and not exposed. The rate of discontinuation due to adverse events was 11.3%, with no differences between the two groups. Conclusions: Our study confirms efficacy and side effects of fingolimod in a second-line clinical practice cohort. Prior natalizumab exposure and duration of treatment with fingolimod are independent predictors of annualized relapse rate during the first 12 months of treatment with fingolimod, but not in the long-term, and may be influenced by the 3 months washout period between the two drugs. © 2014 S. Karger AG, Basel.