Screening for cardiovascular disease risk factors was carried out in 14 of Norway's 19 counties in 1986-1990 as part of a prevention programme. All residents aged 40-42 were invited. The attendance was 73.5% for males and 82.6% for females. A total of 87,761 persons were examined. The screening included determination of serum cholesterol and triglycerides, measurement of blood pressure, height and weight, and filling in a questionnaire. Mean serum cholesterol was 5.90 mmol/l for males and 5.55 mmol/l for females, mean systolic blood pressure 135.3 and 126.1 mm, and prevalence of daily smoking 43.5 and 41.8%. The risk factor levels in the 341 municipalities of the 14 counties are shown cartographically. For both sexes, the highest risk score was found in the northernmost county, the lowest in southern counties. The risk was also relatively high in some rural areas in southern Norway. By geographical area there was a strong correlation between the risk factor levels of the two sexes, and a less consistent but marked correlation between the means for the various risk factors.