Probable and possible MS cases with a debut during the years 1950-1964 within the city of Gothenburg were identified (312 cases). This corresponds to an incidence of 5.3 per 100,000. The material was stratified according to diagnostic probability into three categories. For the final analysis cases with the lowest diagnostic probability were omitted (about 9%). The follow-up was completed during 1977, i.e. 13-27 years from onset. A longitudinal analysis of each case was based upon a mixed prospective/retrospective study in which the authors personally examined the majority of the cases during most of the years. The female/male ratio was 1.5-1.6. The mortality rate was higher for males due in part to an earlier progressive development of multiple sclerosis and in part to a higher trend for acquisition of other mortal diseases. Bouts, as the first manifestation of the disease, were more frequent in young ages than in old, and more frequent among females than in males. The averages bout frequency decreased significantly with the duration of the disease as well as with the age of onset. The opposite trend was characteristic for development of a progressive course. Among symptoms at onset, those indicating lesions of long sensory and/or motor tracts (particularly the sensory) dominated. Such initial symptoms were seen in 30-40% of the younger patients and 70% of the older patients. The rest was divided between cases with optic nerve lesions (20-30% among younger, 12-15% among older patients) and brain stem lesions (approx. 25% among younger, 10-19% among older patients). The occurrence of various symptoms during the first two decades of the disease was also analyzed and the pattern of symptoms presented graphically. These results will be treated further in subsequent studies.