PURPOSE: This study was designed to evaluate the incidence of complication in severely obese children and to determine whether the difference of Lp (a) between severely obese children and normal control group exists. METHODS: Body weight, height and obesity index were measured in 5885 (M:F= 3089:2796) elementary school children. Eight eight (M:F=63:25) were selected as severely obese children. Of the 88 children, 74 agreed to venous puncture for the measurement of serum glucose, total cholesterol, AST, ALT, HDL-cholesterol, apo A1, apo B and Lp (a). Blood pressure and atherogenic index were also checked. Twenty nine children were selected for the control group. RESULTS: The prevalence of severe obesity in elementary school children was 1.5%. Of 74 severely obese children, serum total cholesterol was over 200mg/dl in 16.2%, and HDL cholesterol below 40mg/dl in 47.3%. Atherogenic index was over 3 in 60.8%. The incidence of hypertension and fatty liver was 6.8% and 13.5%, respectively. DM was not found. The levels of total cholesterol, ALT, HDL cholesterol and atherogenic index in severely obese group differed significantly from those of control group. There were no significant differences in apolipoprotein levels between severely obese and control group. CONCLUSIONS: The incidence of complication in severely obese children is considerably high. We need systemic program about obesity prevention and management, and individualized approaches to prevention have to be applied. It seems that severe obesity doesn't directly influence on the levels of Lp (a) and apolipoproteins.