A review of the Rochester, Minn, resident population (provided by the unified record system of the Mayo Clinic) revealed no appreciable increase in the incidence of multiple sclerosis (MS) from 1905 through 1964. Prevalence for the ten-year intervals from 1935 through 1964 was approximately 60 per 100,000 for those with onset in Rochester. Sex-specific incidence and prevalence rates were greater for women, 1.6 to 1.0. The 25-year survival of the MS population was 74% compared to the expected survival of 86% for a group of this age and sex distribution. Two thirds of the surviving patients were ambulatory 25 years after onset. The identification of patients with milder MS through more complete case ascertainment in a community can provide a better prognosis than ordinarily noted in a neurologic clinic or hospital. © 1971, American Medical Association. All rights reserved.