Objective: No current studies have compared North American with European body composition parameters, i.e., fat-free mass (FFM), body fat (BF), and percentage of BF (%BF) in large populations. This study compared FFM, BF, and %BF values derived from two bioelectrical impedance analysis (BIA) equations (Geneva and National Health and Nutrition Examination Survey [NHANES]) in Swiss subjects and compared FFM, BF, and %BF values of white Swiss with those of white North American adults with the same BIA equations. Methods: Healthy adults (3714 men and 3199 women), ages 20 to 79 y, in Switzerland were measured by single-frequency BIA and compared with means and standard deviations for body mass index and body composition parameters obtained from the NHANES III study (United States; n = 2538 men, 2862 women). FFM was calculated with the Geneva and NHANES equations. Results: Mean FFMGENEVA values did not differ from FFMNHANES values in men but was significantly lower (-1.5 kg) in women. FFM and BF values in American men, who weighed 4.2 to 12.0 kg more than the Swiss men, were significantly higher (+2.1 to +6.0 kg and +1.5 to +6.4 kg, respectively) than those in the Swiss men. FFM and BF values in American women, who weighed 2.3 to 12.1 kg more than the Swiss women, were significantly higher (+1.3 to +2.1 kg and +4.8 to +11.8 kg, respectively, except FFM in subjects ages 20 to 29 y and BF in those ages 70 to 79 y) than FFMGENEVA values in Swiss women. FFM in American women was significantly lower (+1.3 and +1.9 kg) and non-significantly higher than FFMNHANES in Swiss women. Conclusion: NHANES and Geneva BIA equations estimate body composition equally well in men, but further research is necessary to determine the discrepancies in FFM between BIA equations in women. The greater weight of the American subjects yielded higher values for FFM, BF, and %BF in American than in Swiss men and women. © 2005 Elsevier Inc. All rights reserved.