OBJECTIVE: The aim of this study was to estimate the influence of tobacco smoking and Swedish snuff use on the risk of developing multiple sclerosis (MS). METHODS: A population-based case-control study was performed in Sweden, using incident cases of MS (902 cases and 1,855 controls). A case was defined as a subject from the study base who had received a diagnosis of MS, and controls were randomly selected from the study base. The incidence of MS among smokers was compared with that of never-smokers. We also investigated whether the use of Swedish snuff had an impact on the risk of developing MS. RESULTS: Smokers of both sexes had an increased risk of developing MS (odds ratio [OR] 1.4, 95% confidence interval [CI] 1.2-1.7 for women, and OR 1.8, 95% CI 1.3-2.5 for men). The increased risk was apparent even among subjects who had previously smoked moderately (