There is a very specific geographic distribution of this disease around the world. A significantly higher incidence of the disease is found in the northernmost latitudes of the northern and the southern hemispheres compared to southernmost latitudes. This observation is based on the incidence of the disease in Scandinavia, northern United States, and Canada, as well as Australia and New Zealand.

The data from migration studies shows that if the exposure to a higher risk environment occurs during adolescence (before 15 years of age,) the migrant assumes the higher risk of the environment. This concept is nicely illustrated in studies of native-born South African white population with low incidence of the disease versus high incidence of MS among white immigrants from Great Britain, where the disease is much more prevalent (Saud A. Sadiq, James R. Miller et al.)

"Epidemics" of MS have been reported and these provide further evidence of importance of environmental factors in MS.  The most notable "epidemic" was described on the Faroe Islands after they were occupied by British troops in W.W.II.  Similar increases in incidence of the disease were seen on Shetland and Orkney Islands, in Iceland, and in Sardinia. A specific "point agent" for these "epidemics" never was identified.