To determine age and ethnic patterns of blood lipid levels in childhood and adolescence and to extend previous adult and late adolescent Israeli data to prepubertal ages, the levels of plasma total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), and triglycerides (TG) were determined among 1,153 schoolchildren in the area of Petah-Tikva. Half of the children were born to immigrants from Yemen. Among boys, TC levels progressively decreased as age increased from 10-11 to 14-15 years (159 to 142 mg/dl). The age-specific TC and HDL-C means among boys are compatible with an initial swift fall with age, followed by a rise restricted to TC during puberty. Among girls, progressively lower means through ages 12-13 and increasingly higher ones for older age groups are also compatible with puberty-determined changes, previously observed in American cohorts. The differences in TC were only partly accounted for by lower HDL-C means at higher ages (52 mg/dl in the youngest and 45 mg/dl in the oldest age group, respectively, among boys, compared with 53 mg/dl for girls at both ages 9 and 16-17). TG levels in boys, but not in girls, showed age differences paralleling those found for HDL-C, but in an inverse direction. TC means were lower as age increased only among female offspring of European-born Jews (159 to 148 mg/dl, ages 9-12 compared with ages 13-17), a phenomenon that requires further study. Overall, TC and HDL-C were clearly higher among girls than boys beginning at ages 12-13, with little or no sex differences in TG. The sex differences in TC, contrary to previous studies, were not fully accounted for by HDL-C sex differences. The ethnic variability paralleled previous findings in Israeli adults and adolescents, showing low TC levels among male offspring of Yemenite and other Asian-born fathers. The ethnic differences among girls were small. No specific pattern of age-related lipid changes was found in the group of Yemenite origin, who represented offspring of parents with notoriously low levels of coronary heart disease incidence.