Because growth and anthropometric measurements are frequently below normal in patients with cystic fibrosis (CF), the body composition of 23 children (6-9 y of age) who had mild manifestations of CF was examined and compared with a control group of 24 subjects similar in age, sex, and weight. Skinfold measurements, total body water (TBW) by deuterium oxide dilution, and total body electroconductivity (TOBEC) were measured. Skinfold and TBW measurements demonstrated that fat mass and fat-free mass did not differ significantly between the two groups. No significant difference in percent body fat was found by using the skinfold equations of Slaughter et al (13.8% vs 15.3%), although percent body fat (TBW method) differed between the groups (P < 0.05). TOBEC measurements (CF, n = 14) were not used in the group comparison. The majority of the methods demonstrated that the CF group achieved normal growth and body composition, with a possible trend of fat depletion.