The associations between age, sex, height, Quetelet index, blood pressure, and serum cholesterol level were examined among 1406 routinely screened children, aged 4 to 19 years, in a pediatric practice. After adjustment for sex and age, height and Quetelet index were associated with serum cholesterol levels. Quetelet index was shown by multiple linear regression to be positively related to cholesterol levels (b = 0.780, P < 0.01), but the predictive value of screening based on an elevated Quetelet index was marginal. Clustering of elevated serum cholesterol level, Quetelet index, and systolic blood pressure was observed. Familial aggregation of cholesterol levels was demonstrated using analysis of variance for 742 children from 342 families included in the regression analysis (F341,400 = 1.56, P < 0.0001). The intraclass correlation coefficient, a measure of familial aggregation, was 0.205 (P < 0.0001). Age, sex, height, Quetelet index, and familial aggregation accounted for 10.6% of the variance in serum cholesterol levels. Siblings of children with high cholesterol levels are a high-yield group in cholesterol screening.