Abstract Serum low-density lipoprotein (LDL) particles vary in size, composition, and atherogenic potential. Relationships between the ratio of cholesterol to apolipoprotein B (apo B) within LDL, and levels of other lipoprotein variables in serum were examined in a biracial (black-white) sample (N = 2,053) of 8- to 17-year-olds whose median triglyceride level remained relatively low (56 mg/dL). The LDL cholesterol to apo B ratio showed a significant positive association with high-density lipoprotein (HDL) cholesterol ( r = .36 to .44), HDL 2 cholesterol ( r = .34 to .50), HDL 3 cholesterol (in whites only, r = .24 to .28), and apo A-I ( r = .17 to .27), and a significant inverse association with triglycerides (except in black girls, r = −.15 to −.19). The best predictor of the LDL cholesterol to apo B ratio was HDL cholesterol or HDL 2 cholesterol in all four race-gender groups; triglycerides entered as a predictor variable only in black boys. Since relationships of LDL and HDL to coronary heart disease (CHD) risk are considered interdependent, a subgroup of children with apo B-enriched LDL and low HDL cholesterol may be potentially at increased risk.