Concussion is associated with multiple sclerosis if it occurs before infectious mononucleosis.

The objective here was to examine if concussion before or after infectious mononucleosis during adolescence is differently associated with multiple sclerosis risk.

Using national Swedish health registers, among those born from 1980 with follow-up to 2023, we identified a cohort with infectious mononucleosis between ages 11 and 20 years among people without a demyelinating disease diagnosis by age 20 years ( n = 37 432), among whom 174 had a subsequent multiple sclerosis diagnosis.