The incidence of multiple sclerosis (MS) in nurses during the period 1980-1996 was calculated in a nationwide study. The cohort consisted of 69,428 nurses, 2185 men and 67,243 women. Sixty (two men and 58 women) with definite MS were observed, whereas 69.3 were expected. We found no significant difference between the observed and expected number of MS cases (standardized incidence ratio = 0.87; 95% confidence interval, 0.66-1.12).