The analysis of serum lipoprotein was performed in school children in suburban areas in Japan. Serum lipid levels and lipoprotein profiles of obese children were compared to those of controls with normal body weight. Obese children with body weight more than 20 per cent above ideal body weight comprised approximately 6 per cent of the children. There was little difference in concentration of total cholesterol and triglycerides between the obese and the non-obese children. However, in obese children, the level of HDL-cholesterol was significantly lower and the level of (VLDL + LDL)-cholesterol was higher, so that the ratio of (VLDL + LDL)-cholesterol to HDL-cholesterol was substantially higher than in non-obese children. In the obese children, a linear correlation was obtained between total serum cholesterol and the ratio of (VLDL + LDL)-cholesterol to HDL-cholesterol level, which showed the increase of HDL-cholesterol was not accompanied with the increase of total cholesterol, while in the non-obese children, total serum cholesterol was not parallel with the ratio of (VLDL + LDL)-cholesterol to HDL-cholesterol level, suggesting a co-increase of HDL-cholesterol with LDL-cholesterol. As the changes in lipoprotein profiles characterized by the increase in LDL and the decrease in HDL is one of the major risk factors of atherosclerosis, the prevention of obesity during school life seems to be important to prevent atherosclerotic diseases even in normolipidemic children.