The experience of the treatment of patients with remitting multiple sclerosis (MS) with intramuscular introduction of beta-interferon-1a (avonex) is presented. Seventeen children and adolescents, aged from 11 to 18 years, and 55 adults, aged over 55 years, were treated for at least one-year period. Results revealed a significant reduction of exacerbations in both groups (from 1.35 to 0.06 in average in adolescents and from 0.86 to 0.17 in adults). The changes were accompanied by the stabilization of MS severity index: EDSS scores have decreased in 23.6% of adults and in 17.6% of adolescents. In both groups, good tolerability of the treatment was noted. There was a low probability of side-effects with the exception of increased frequency of a flu-like syndrome (47% cases) in patients younger than 18 years that demands special attention from children neurologists. The high efficacy and good tolerability and safety profile of beta-interferon-1a give grounds for administering this drug to children and adolescents with MS.