Reports on adverse neurologic events after application of vaccines produced concern about vaccinations such as those against hepatitis B. The question is raised whether infectious agents or vaccines are involved in the pathogenesis or induce worsening of multiple sclerosis (MS). In the past few years, evidence has been provided that a single T cell is capable of recognizing several antigens. Thus, the possibility of activating autoantigen-specific T cells by pathogens or vaccines is raised. Very recent epidemiologic studies presented here have however demonstrated that the risk of MS is not elevated in hepatitis B-vaccinated individuals and that the course of MS is not worsened by hepatitis B, tetanus, or influenza vaccinations.