The results of using ronbetal, the Russian biosimilar of interferon-beta 1b, in the treatment of multiple sclerosis (MS) are presented. The study included outpatients followed up from February 2008 to March 2012. All patients were assessed neurologically with additional evaluation using the EDSS; a number of exacerbations and their outcomes, disease progression, tolerability of the drug were recorded. No significant differences in the efficacy of ronbetal and betaferon were found. The frequency of exacerbations and MS progression were comparable for both drugs. The same was with the tolerability, with the exception of higher frequency of the flu-like syndrome at the beginning of treatment with ronbetal. A single-step substitution of betaferon for ronbetal often caused the discontinuation of treatment by patients because they were not fully informed about the new drug, need to use a new dose titration scheme and were anxious about side-effects.