The clinical features of multiple sclerosis (MS) in north-east Scotland have been examined along with an epidemiological study to determine the prevalence of the disease on 1st December, 1970. Patient information was collected from all available diagnostic indices, both retrospectively and prospectively from 1965. Every family doctor in the region contributed. The age and sex specific prevalence rates for MS in north-east Scotland on 1st December, 1970, are the highest ever recorded. Among the 80,000 women aged 40 to 69, one in every 340 had the disease. The mean incidence rate for a 12-year period was 5.0/100,000. A significantly better prognosis with regard to disability was found for onset with sensory symptoms, a relapsing/remitting type of course, men with long disease duration, and an initial remission period of 4 or more years. The occurrence of various abnormal neurological signs and symptoms has rarely been recorded in a large epidemiological study. The findings in this study, however, are similar to previous non-epidemiological studies.