The dose-exposure-response relationship for drugs may differ in pediatric patients compared with adults. Many clinical studies have established drug dose–exposure relationships across the pediatric age spectrum; however, genetic variation was seldom included. This article applies a systematic approach to determine the relative contribution of development and genetic variation on drug disposition and response using HMG-CoA reductase inhibitors as a model. Application of the approach drives the collection of information relevant to understanding the potential contribution of ontogeny and genetic variation to statin dose-exposure-response in children, and identifies important knowledge deficits to be addressed through the design of future studies.