On the basis of a longitudinal study of growth in French children, we attempted to find a valid index for estimating adiposity, and to specify the optimal conditions for its use. The Quetelet index was found suitable for application to children, but as with all methods, a certain lack of precision proved unavoidable because of the different stages of growth observed at a given age. For use by clinicians, we provide charts, based on the Quetelet index and on age, permitting estimation of adiposity in any child on the basis of longitudinal study measurements. For use by epidemiologists, we give standard values for studying groups of subjects, even when a reference population is not available. Body adiposity may be expressed independently of age and sex.