['To assess the prevalence and the profile of adverse events (AE) of natalizumab in patients with multiple sclerosis (MS).', 'Data collection from neurologists attending to patients with MS at specialized units in Brazil.', 'Data from 103 patients attending the infusion centers of 16 MS units in 9 Brazilian states were included in the study. The total number of infusions was 1,042. Seventy-nine patients (76.7%) did not present any AE. Twenty-four patients (23.3%) presented only mild AE. There were three major AE, including two deaths. These three occurrences, although not necessarily being drug-related, must be taken into consideration.'] Are natalizumab adverse events rare in patients with multiple sclerosis?