In a group of 2000 Prague children aged 11-12 years the distribution of serum cholesterol levels was assessed. For further investigations 100 children with cholesterol levels above the 95th percentile (HYPER) were selected and 100 children with values between the 5th and 10th percentile (HYPO). Children and parents were subjected to detailed clinical and laboratory examination, in children the three-day dietary intake was assessed. Boys of the HYPER group had significantly higher LDL, HDL and VLDL cholesterol levels as well as levels of apolipoprotein B and less favourable values of the atherogenic index (AI). Girls of the HYPER group had significantly higher mean values of LDL-cholesterol and apolipoprotein B and also less favourable values of the AI. In the group HYPER children no abnormalities were detected in the carbohydrate metabolism nor a higher incidence of obesity although they differed significantly from children in the HYPO group as regards parameters of the lipid spectrum. The energy value of the consumed diet of children in the HYPER and HYPO group does not differ significantly. Although in boys of the HYPER group there was a higher ratio of total fat and animal fat (p less than 0.05), neither the percentage ratio of fatty acids nor the P:S ratio differed significantly in children of the HYPER and HYPO group. Parents of children of the HYPER group had significantly higher mean cholesterol, apolipoprotein B, LDL cholesterol values and less favourable values of the atherogenic index than parents of children of the HYPO group. The incidence of hypercholesterolaemia in the families of these children was also significantly higher.