In 1993, interferon beta-1b (IFN beta-1b, Betaferon/Betaseron) was the first interferon approved in the USA for relapsing-remitting multiple sclerosis (RRMS). Since then, dose-dependent effects of IFN beta in MS have been extensively discussed. Such effects had already been observed in the pivotal trial and were followed by dose comparison trials with IFN beta-1a. Later, the therapeutic efficacy of IFN beta-1b could also be demonstrated in secondary progressive (SP) MS patients. We learnt from further studies that benefit from IFN beta in SPMS seems to be most pronounced in those patients still having active disease with superimposed relapses or clear progression. The most common IFN beta-related adverse events, especially in the early treatment phase, have been flu-like symptoms and injection-site reactions. The consequent management of those as well as of other, less frequent, side-effects turned out to be of tremendous importance to ensure patients' compliance. Based on the experience of 10 years, IFN beta-1b belongs to the firstline therapeutics in RR and SPMS.