The relation of obesity to clustering of systolic blood pressure, fasting insulin, and ratio of low and very low density lipoprotein cholesterol to high density lipoprotein cholesterol [LDL-C + VLDL-C)/HDL-C) was investigated in 3,503 subjects aged 5-24 years in Bogalusa, Louisiana, from September 1981 to September 1983. Risk ratios (RR) were calculated as the number of subjects with risk factor variables in the upper tertile divided by the expected number. The variables showed strong clustering (RR = 3.1); however, after adjusting for obesity, clustering of systolic pressure, (LDL-C + VLDL-C)/HDL-C, and insulin was reduced (RR = 1.3). Lean subjects (lower tertile of obesity) showed less clustering than expected (RR = 0.4), while more obese subjects (upper tertile of obesity) had greater clustering than expected (RR = 3.1). Furthermore, trunk fat deposition (subscapular skinfold) had a greater impact on clustering at high levels than limb fat deposition (triceps skinfold). Since obesity is related to clustering of risk factor variables in children and young adults, the prevention of the onset of obesity in early life may be important to reducing the risk of coronary heart disease in later life.