Serum and CSF NFL concentrations correlated weakly with EDSS (ρ = 0.380, 95% confidence interval [CI] 0.297–0.457, p < 0.001; and ρ = 0.243, 95% CI 0.153–0.329, p < 0.001, respectively) and with Multiple Sclerosis Severity Score (ρ = 0.392, 95% CI 0.310–0.468, p < 0.001; and ρ = 0.340, 95% CI 0.255–0.420, p < 0.001, respectively). Here, NEFL is linked to multiple sclerosis.