The aim of this study was to identify factors influencing the long-term clinical progression of multiple sclerosis (MS). A special objective was to investigate whether early treatment decisions influence outcome.

We included 639 patients diagnosed with MS from 2001 to 2007. The median follow-up time was 99 months (8.25 years). Cox regression models were applied to identify factors correlating with the outcome variable defined as time from treatment start to irreversible score 4 of the Expanded Disability Status Scale (EDSS).

Patients initiated on treatment later had a greater risk of reaching EDSS 4 (hazard ratio of 1.074 (95% confidence interval (CI), 1.048–1.101)), increased by 7.4% for every year of delay in treatment start after MS onset. Patients who started treatment after 3 years from MS onset reached the outcome sooner with hazard ratio of 2.64 (95% CI, 1.71–4.08) compared with the patients who started treatment within 1 year from MS onset. Baseline EDSS and age at onset were found to be predictive factors of disability progression.

Early treatment initiation was associated with a better clinical outcome. In addition, we confirmed the well-established prognostic factors of late age at onset and early disability.