Controversy exists regarding the predictive value of the early clinical course of multiple sclerosis (MS). Three parameters often considered are the attack rate, the first interattack interval and the rate at which disability develops in the early years of the disease. We have recorded the time to reach successive levels of disability defined by the Kurtzke Disability Status Scale (DSS) in 1,099 MS patients followed at University Hospital, London, Canada between 1972 and 1984. Our population is particularly suitable because of its size, the high degree of ascertainment of cases in the community, and the regular follow-up provided. Life table analysis was used to compare survival in patients stratified according to the above three parameters using DSS 6 as end point. Significant differences were evident in the survival distributions. Despite the extensive interindividual variation in the rate at which disability developed, the early course of MS may be useful in determining the relative risk of rapid progression.