Objective:To prospectively investigate the association between dietary sodium intake and multiple sclerosis (MS) risk.Methods:In this cohort study, we assessed dietary sodium intake by a validated food frequency questionnaire administered every 4 years to 80,920 nurses in the Nurses' Health Study (NHS) (1984–2002) and to 94,511 in the Nurses' Health Study II (NHSII) (1991–2007), and calibrated it using data from a validation study. There were 479 new MS cases during follow-up. We used Cox proportional hazards models to estimate hazard ratios (HR) and 95% confidence intervals (CI) for the effect of energy-adjusted dietary sodium on MS risk, adjusting also for age, latitude of residence at age 15, ancestry, body mass index at age 18, supplemental vitamin D intake, cigarette smoking, and total energy intake in each cohort. The results in both cohorts were pooled using fixed effects models.Results:Total dietary intake of sodium at baseline was not associated with MS risk (highest [medians: 3.2 g/d NHS; 3.5 g/d NHSII] vs lowest [medians: 2.5 g/d NHS; 2.8 g/d NHSII] quintile: HR_pooled 0.98, 95% CI 0.74–1.30, p for trend = 0.75). Cumulative average sodium intake during follow-up was also not associated with MS risk (highest [medians: 3.3 g/d NHS; 3.4 g/d NHSII] vs lowest [medians: 2.7 g/d NHS; 2.8 g/d NHSII] quintile: HR_pooled 1.02, 95% CI 0.76–1.37, p for trend = 0.76). Comparing more extreme sodium intake in deciles yielded similar results (p for trend = 0.95).Conclusions:Our findings suggest that higher dietary sodium intake does not increase the risk of developing MS.