We present fractile data on serum lipids and apolipoproteins A-l and B for children and young adults from the cardiovascular risk in young Finns study cohort of 1986. The sample comprised 2370 fasting children and young adults (1114 males and 1256 females) aged 9, 12, 15, 18, 21 and 24 years. The determinations were performed in duplicate with standard methods. LDL-cholesterol values were calculated. The limits for clearly pathological values (exceeding the 97.5th percentile) irrespective of age and gender were 7.5 mmol/l, 5.0 mmol/l, 3.5 mmol/l and 1.4 g/l for serum total cholesterol, LDL-cholesterol, triglycerides and apolipoprotein B, respectively. Corresponding values (below the 2.5th percentile) for HDL-cholesterol, apolipoprotein A-l, HDL2- and HDL3-cholesterol were 0.80 mmol/l, 1.0 mg/l, 0.20 mmol/l and 0.70 mmol/l, respectively. Approximately 79%, 33% and 7% of males had serum total cholesterol values greater than 4.0 mmol, 5.0 mmol/l and 6.0 mmol/l, respectively. Corresponding percentages for females were 87%, 43% and 10%. However, age-related differences were marked. The prevalence of values, e.g. greater than 6 mmol/l according to age, ranged from 6 to 13% in females and from 3 to 12% in males, emphasizing the need for age-specific reference values. Additionally, postpubertal values for total and LDL-cholesterol tended to be slightly lower compared to prepubertal values, indicating that the reference values for adults do not apply to adolescents and young adults. The age-related changes in lipid levels were evident in each fractile and were especially accentuated in higher fractiles. Fluctuations with age were more pronounced in males than in females. These results are intended to be applied as reference values for diagnosing dyslipidemias.