Body mass index (BMI), the distribution of fat, birth weight, physical fitness, apolipoproteins (apo) A-I and B, total cholesterol (TC), and high-density lipoprotein cholesterol (HDLC) were studied in 38 obese 10- to 11-year-olds in comparison to 52 age-matched controls. Obese children had higher concentration of apo B and a lower apo A-I:B ratio. Significant correlations were found between (a) apo A-I and physical fitness (r = 0.35, p less than 0.015), triceps skinfold thickness (r = 0.44, p less than 0.01), and birth weight (r = -0.33, p less than 0.05); (b) physical fitness and triceps skinfold thickness (r = 0.38, p less than 0.05), and (c) the apo A-I:B ratio and triceps skinfold thickness (r = 0.31, p less than 0.05). When both obese and control children were grouped together, a correlation was found between BMI and TC (r = 0.24, p less than 0.05), apo B (r = 0.37, p less than 0.001), and the apo A-I:B ratio (r = -0.31, p less than 0.01). Multiple regression analyses indicated a significant positive contribution to the apo A-I level by HDLC and physical fitness and a negative one by birth weight.