Cardiovascular risk factor levels among 40-year olds in Oslo were studied from the early 1970s until the late 1980s. Comparison has been made with similar data for the same period from two other regions in the country. The serum cholesterol level in men decreased from 6.3 mmol/l in 1972-73 to 5.9 mmol/l in 1985-88 and the proportion of men who smoked on a daily basis decreased from 51.8% to 40.8%. The proportion of female smokers increased from 37.4% in 1981-84 to 39.5% in 1985-88. There was a decrease in systolic blood pressure among men from 1972-73 to 1985-88. From 1981-84 to 1985-88 there was a minor increase for both sexes in the proportion of physically inactive for both sexes or those with a body mass index > 30. Prior to 1980 cardiovascular risk factors were most favourable in Sogn og Fjordane, and least favourable in Finnmark, with men from Oslo positioned somewhere in between these counties. With the exception of women's smoking habits and, for both sexes, the degree of physical activity, people living in Oslo in 1985-88 had a more favourable risk factor status than those in Sogn og Fjordane in 1985 and in Finnmark in 1987. Despite a degree of uncertainty because of methodological issues, the results indicate a reduction in risk factors of cardiovascular disease among men in Oslo during the 15 years covered by the study.