Prevalence studies carried out in Sardinia from 1975 suggest an increasing occurrence of MS. However, it is questionable whether this increase represents a real change in MS incidence or simply reflects longer survival. Data from 79 patients indicated the average annual incidence for the period 1965 through 1985 was 3.4 per 100,000. On December 31, 1985, the prevalence rate was 69 per 100,000. Evaluation of MS temporal trends showed a significant increase in MS incidence during the study period: values ranged around two per 100,000 in the triennial periods 1965-1967, 1968-1970, and 1971-1973, and around five in each triennium from 1977 onward.