A prospective epidemiological study of multiple sclerosis (MS) has been conducted in Novosibirsk with the following analysis of MS prevalence and incidence and estimation of the disease frequency in different age groups. The wave-like change of MS incidence within 1.5-2.5 per 100,000 persons was observed from 1970 to 2002, with a trend to decreasing, in particular among men, over the last decade. At the same time, there was an increase of MS prevalence (from 29.2 in 1984 to 54.4 in 2003) combined with increasing of illness duration and a fraction of slowly progressive MS variants.