A total of 638 new cases of multiple sclerosis (MS) (365 females, 273 males) were found from 1970-1984 in northern Greece (Macedonia and Thrace); the average annual incidence rate was 1.79 per 100,000 inhabitants with increasing incidence from 1980-1984. A total of 729 people living in northern Greece suffered from MS on December 31, 1984 (prevalence rate 29.5 per 100,000 inhabitants). No difference was found between urban and rural areas. No difference from the international standards was found for sex incidence. The study confirms the quite high prevalence of MS despite the fact that northern Greece is in the intermediate risk zone.