Since 1974 we have attempted to ascertain all cases of MS beginning 1900–1975 in Iceland. As of October 1979 they numbered 168; all but 5 met all diagnostic criteria of the Schumacher Committee. Virtually all cases had been examined by at least one of the authors. Cases were few and sporadic from 1900 to 1922, then increased to a plateau for 1923–44, then again increased in 1945 with an irregular plateau thereafter.

Average annual incidence rate for 1945–1954 was 3.2 per 100,000 population, significantly higher than the 1.6 for 1923–1944 or the 1.9 for 1955–1974. Age at onset was significantly decreased for cases with onset 1945–1949 and then sharply increased for those with 1950–1954 onsets. The occurrence of MS in 1945–1954 meets the criteria for a point-source epidemic, whose tail thereafter merged into what may be “baseline” for Iceland. This postwar epidemic is then similar to that recently described for the Faroe Islands, a land that shares its history, culture, and peoples with Iceland.