In this issue of Neurology®, Høglund et al.1 report an association between higher body mass index (BMI), especially among a younger population (14–24 years of age) and the long-term risk of developing multiple sclerosis (MS). The authors harnessed the Norwegian national tuberculosis screening program, which objectively measured height and weight in a population that represented 85% of the population of Norway in years 1963 to 1975. The study linked the calculated BMI with data from the Norwegian MS registry, which has been registering patients with incident-onset MS since 2001, with close to 70% coverage of the national MS cohort, and separately with the Norwegian Cause of Death Registry. The authors identified 1,409 persons at the onset of MS among the population of 648,734 individuals 14 to 34 years of age who had participated in the tuberculosis screening program. Both women and men who were obese (≥95th percentile of BMI) during adolescence and early adult life (14–24 years) were 1.5 times more likely to develop MS than those with normal weight. The study did not find evidence for increased susceptibility to MS among individuals with high BMI at 25 to 34 years of age, potentially due to the relatively small number of either obese or incident-onset MS cases in this group.