A comprehensive study of coronary heart disease (CHD) risk factors and their determinants in children and adolescents in Finland was initiated in the late 1970's. The main cross-sectional study was undertaken in 1980, with 3596 subjects aged from 3 to 18 years participating. The first follow-up study was carried out in 1983, and the second in 1986. The present report describes briefly some findings in 2746 children and young adults, aged 9, 12, 15, 18, 21 and 24 years, participating in 1986. Serum total cholesterol concentrations, mean (SD), ranged between 4.31 (0.73) and 4.91 (0.81) mmol/l in boys, and between 4.73 (0.85) and 5.09 (0.82) mmol/l in girls, respectively. Mean serum cholesterol values had fallen from 1980 to 1986 by 5.4% in such age cohorts, which had been included in all three studies. Fat content in the diet remained unchanged (38 E %), whereas the mean P/S ratio increased from 0.24 in 1980 to 0.31 in 1986. Young Finns from East Finland had a higher somatic risk index than those from West Finland (P greater than 0.001). The clustering of somatic risk factors was stable between 1980 and 1986. Further follow-up of the cohorts will, we hope, provide the tools for implementing primary prevention of CHD in Finland.