Evidence shows that serum neurofilament light chain (sNfL) levels are elevated in multiple sclerosis (MS). NfL is released in response to neuronal injury and in MS, it has been associated with measures of disease activity, disability worsening and brain atrophy. Elias Sotirchos, MD, Johns Hopkins University School of Medicine, Baltimore, MD, discusses a real-world multicenter cohort study of patients and healthy controls enrolled in the MS PATHS network, designed to assess the associations of sNfL with disease features in MS. The results showed raised sNfL to be associated with worse neurological function and brain atrophy, as well as with progressive MS and comorbidities such as diabetes and smoking. Further analysis may allow validation of sNfL levels as a biomarker in MS. This interview took place during the ACTRIMS Forum 2021.