[Occurrence of multiple sclerosis in Nordland, 1970-1999].
Epidemiologic data for multiple sclerosis in Nordland County in Norway has not been recorded for more than 50 years. Cases between 1970 and 1999 were identified by diagnostic code searches in the files of Nordland Central Hospital, the county's only hospital with a department of neurology. Several cases from Nordland were also identified in hospital files in neighbouring counties. The raw prevalence of multiple sclerosis was determined to be 105.6 per 100,000 as at December 31, 1999. The crude annual incidence in the 1970-1999 period was 3.6 per 100,000 (95 % CI: 3.1-4.0). There was a pronounced rise in incidence from the late 1970s up until the early 1980s. From 1985 to 1999, the average annual incidence rate has been stable at 5.1 per 100,000 (95 % CI: 4.4-5.8). Compared to other Norwegian counties for which there are epidemiologic data, Nordland represents a medium risk zone for multiple sclerosis. The increase in incidence from the late 1970s to the early 1980s is most likely due to improved diagnosis and better record-keeping.