The oversimplified but commonly accepted belief, based on the comparison of the prevalence studies conducted until 1980, that the distribution of multiple sclerosis (MS) in Europe is related to latitude has been contradicted by a great number of prevalence and incidence studies carried out since 1980. The most recent studies, based on more appropriate methods, clearly indicate that the MS distribution in Europe is much more complex than supposed in the past. The MS distribution in Europe now appears to be very uneven, with great variations not only between areas at the same latitude, but also within the countries themselves. However, even the most recent European studies cannot be reliably compared because of differences in the denominator characteristics, case ascertainment accuracy, diagnostic criteria, and definitions of prevalence and incidence. Despite these problems, descriptive data since 1980 indicate that ethnicity plays an important role in determining the European MS distribution. Furthermore, variations in both prevalence and incidence rates in ethnically homogeneous populations confirm the i importance of environmental factors in determining the primary acquisition of the disease. Further descriptive studies based on more comparable methods and better control for ethnicity would more precisely define the role of genetic susceptibility as well as suggest more valuable clues regarding environmental factors affecting the primary acquisition of MS.