The North Karelia Project, a community-based demonstration project for prevention of cardiovascular diseases since 1972 in Finland, was successful in reducing the population levels of the major cardiovascular risk factors. A net decline in risk factors and coronary heart disease mortality was observed in North Karelia in the 1970s. Thereafter, the mortality from coronary heart disease has declined markedly in all of Finland. The aim of the study was to find out how the cancer mortality has changed in North Karelia during this longer follow-up period. Age-adjusted mortality trends were calculated for the male population aged between 35 and 64 years in the province of North Karelia, and in all of Finland for the period 1969-91, using the official mortality data. The trends and the changes were calculated using general linear model procedures. During the 20-year period, cancer mortality declined in North Karelia by 45.4% and in all of Finland by 32.7% (P = 0.006 for difference). The greater decline in North Karelia occurred particularly in the second decade of the follow up, and lung cancer. The results support the hypothesis that reduction in the population levels of the cardiovascular risk factors lead to beneficial changes in cancer mortality rates, but such changes take longer time to manifest than for coronary heart disease.