Objectives: Natalizumab long-term effectiveness data in real-world relapsing-remitting multiple sclerosis (RRMS) is needed. Our objective is to report the long-term effectiveness and safety of natalizumab in a cohort of RRMS patients. Methods: This is a retrospective study of natalizumab treatment for two years or longer in RRMS. Annualized relapse rate, Expanded Disability Status Scale (EDSS), brain magnetic resonance imaging T2 lesion volume, JC virus antibody status, previous treatments and adverse events were analysed. Results: Seventy-one patients were included with a mean treatment duration of 44.86 +/- 17.39 months. Over the treatment duration there was a significant decrease in annualized relapse rate (88.37%) and EDSS (28.57%); no evidence of clinical disease activity in 73.24% and 61.97% after one and two-years respectively; and brain magnetic resonance imaging T2 lesion volume remained stable. Forty patients suspended natalizumab, in 85% due to high risk of developing progressive multifocal leukoencephalopathy (PML). The major complication was PML (n = 3). Conclusions: Natalizumab showed effectiveness in the long-term follow up period of our cohort, with reduction of ARR, EDSS, and MRI lesion load stabilization. PML was the major complication. (C) 2017 Elsevier B.V. All rights reserved.