Multiple sclerosis in the two northernmost counties of Norway

The prevalence of MS in the two northernmost counties of Norway increased from 20.6 per 100,000 in 1973 to 31.5 per 100,000 in 1983, the increase being most marked in women. The average annual incidence seems to have been stable over the past 20-30 years. None of the patients had a pure Lapp background (having a Lapp mother and father).