Obesity is a prevalent childhood condition and the degree of adiposity is likely to be an important covariate in the pharmacokinetics (PKs) of many drugs. The goal of these studies was to facilitate the evaluation and, where appropriate, quantification of the covariate effect of body fat percentage (BF%) on PK parameters in children. Researchers examined two large databases to determine the values and variabilities of BF% in children with healthy body weights and in those with obesity, comparing the accuracy and precision of BF% estimation by both clinical methods and demographically derived techniques. They also conducted simulation studies to evaluate the utility of the several methods for application in clinical trials. The estimation of BF% from sex and obesity stage can routinely be applied to PK clinical trials to evaluate the contribution of BF% as a potential covariate.