Course and possible prognostic predictors were studied retrospectively in 363 MS patients collected during an epidemiological study. The proportion of patients showing a primarily progressive course was 18%; 19% of patients of more than 10 years duration showed a benign course, and 8% of those of less than 16 years duration, a malignant course. Although benign cases were twice as frequent in females as in males, the difference between both sexes was not significant. A primarily or secondarily progressive course, a high number of functional systems involved and cerebellar signs occurring in the course indicated a poor prognosis whereas symptoms at onset, age at onset as such, and occupation were without predictive value. No predictors of a favourable course were found. Of the patients of 11-15 years duration, 17% were confined to a wheelchair, 40% were restricted to a walking distance of 500 metres or less, 61% were unable to work and 45% had urinary incontinence. The corresponding figures for those of 21-25 years duration were 40%, 71%, 76% and 50%.