This retrospective cohort study assessed the timing of infusion-related adverse events (IAEs) during natalizumab (NTZ) administration in well-documented relapsing-remitting multiple sclerosis (RRMS) patients who had received NTZ infusions in our centre between 2006 and 2018. In 225 RRMS patients (14,174 NTZ infusions), 276 IAEs (1.95%) occurred in 60 patients. All documented severe IAE occurred during infusion. Of the 19 moderate adverse events, 17 were during infusion. None of the reactions that occurred after the infusion required intervention. These results suggest that post-infusion monitoring is not necessary in patients who do not have an adverse event during infusion.