Nutrient intake and serum total cholesterol (C T), serum high density lipoprotein cholesterol (HLD), triglycerides (TG) and fatty acids were evaluated from 692 3-year, 8-year and 12-year-old children in different areas in Finland. Serum/plasma TC concentrations varied from 4.8 to 5.0 mmol/l, HDL from 1.3 to 1.5 mmol/l and TG from 0.70 to 0.87 mmol/l. 12-year-old boys consumed significantly more energy than girls at the same age. In the 8-year-old boys the quality of fat used on the bread and quality of milk drunk influenced on the serum fatty acid composition, the proportion of linoleic acid being greater in those children who used margarine and/or low fat milk. The 3-year-old children at the highest quartiles of TC concentration used less wheat products and their intake of riboflavin was less than children in the lowest quartile. HDL concentration was associated with the intake of thiamine. The 12-year-old children having their TC concentrations in the highest quartile used more saturated fats and got more saturated fatty acids than children in the lowest quartile. The higher the sugar consumption and sucrose intake were, the lower was the HDL concentration. The prevalence of obesity increased with the age, being 0.5%, 5.0% and 8.5% in the 3-year, 8-year and 12-year-old children respectively. Urban children were more commonly obese than rural children, the prevalence being 8.0% versus 2.2% (p less than 0.01).