The purpose of this report was to assess intrafamilial associations of lipids between related and unrelated household members seen in the course of a population-based survey of lipids in schoolchildren and their parents. Fasting plasma total cholesterol and triglyceride levels were measured in 6,857 and 3,079 adults. Age effects were removed for each sex-race group using a third-degree polynomial regression of lipid on age; the residuals were then used as observations in the analyses. For both cholesterol and triglyceride, significant positive correlations existed between father and son, father and daughter, mother and son, and mother and daughter. For both cholesterol and triglyceride, although the mother-child correlations were stronger than those for father-child, they were not significantly different. There were no significant correlations between step, foster, or adoptive parents and children. For cholesterol in sibships of size two, intrasibship correlations for fully related siblings were 0.333, for half-sibs 0.164, and for unrelated sibs, 0.085. Consistently closer intrafamilial cholesterol and triglyceride associations between related than unrelated family members, and the strong parental effects on cholesterol and triglyceride indicate, in aggregate, that a considerable proportion of the variation of cholesterol and triglyceride can be explained by genetic factors.