A comparison of blacks and whites 6 to 49 years old revealed striking differences between races with respect to the prevalence of various dyslipoproteinemias and mean plasma lipid levels. Compared with whites, juvenile and adult blacks of both sexes had higher mean levels of high-density lipoprotein cholesterol (HDL-C), with correspondingly higher prevalences of the hyperHDL and hypoLDL (low-density lipoprotein) phenotypes. In contrast, whites showed a much higher prevalence of type IV hyperlipoproteinemia and higher mean triglyceride levels in most age-sex groups. Although juvenile blacks had higher mean levels of LDL-C than did whites, this race difference was reversed in men, while women showed inconsistent differences between races. Adult black men and juvenile blacks of both sexes had a somewhat higher prevalence of the type IIA phenotype than whites. The distribution of major HDL-C predictors in this population could not account for the difference in prevalence of hyperHDL between races. These findings suggest that health professionals may find differences in plasma lipid and lipoprotein patterns between their black and white patients, but additional research is needed to ascertain the disease risks associated with dyslipoproteinemia among blacks.