Prognosis of multiple sclerosis is highly variable. Clinical variables have been identified that are assessable early in the disease and are predictors of the time from the disease onset to the onset of irreversible disability. Our objective was to determine if these clinical variables still have an effect after the first stages of disability have been reached. We determined the dates of disease onset and assignment of scores of irreversible disability in 1844 patients with multiple sclerosis. We used three scores on the Kurtzke Disability Status Scale as benchmarks of disability accumulation: 4 (limited walking but without aid); 6 (walking with unilateral aid); and 7 (wheelchair bound). We used Kaplan-Meier analyses and Cox regression models to determine the influence of the clinical variables on the time to disability onset. Median times from onset of multiple sclerosis to assignment of a score of 4, 6 and 7 were significantly influenced by gender, age, symptoms and course (relapsing-remitting or progressive) at onset of the disease, degree of recovery from the first relapse, time to a second neurological episode, and the number of relapses in the first 5 years of the disease. Similarly, times from onset of multiple sclerosis to a score of 6 and 7 were influenced by time to a score of 4. In contrast, none of the variables substantially affected the time from a score of 4 to a score of 6 or 7, or from a score of 6 to a score of 7. Early assessable clinical variables significantly influence the time from the onset of multiple sclerosis to the assignment of a disability score of 4, but not the subsequent progression of irreversible disability.