A method is presented for assessing childhood obesity in a more objective way than most other routine methods used for diagnosing childhood obesity. The sum of bicipital, tricipital, subscapular, and suprailiacal skinfold thicknesses is related to total body density by use of theoretically defined prediction equations. Total body density is used to estimate total body fat percentage by use of age- and sex-dependent equations on the relation between body fat percentage and body density. These equations are constructed on the basis of published data on changes in the density of fat-free mass with age in children. With the proposed method childhood obesity can be assessed routinely in a more consistent way than with most other routine methods used to diagnose obesity in children. A preliminary validation study indicated that in children aged 7-10 y predicted body density differed on average less than 1% from measured body density. In addition, predicted body density was highly correlated (r greater than 0.7) with measured body density.