Ethical concerns and medical advances unique to children and adolescents make pediatric research an evolving endeavor. The child's changing physiology from infancy to maturity requires understanding of the benefits and risks of medical therapies currently available, but often not tested in children, as well as the risks and benefits of inclusion of children in clinical research. Recent mandates from the US Food and Drug Administration (FDA) require that drugs be tested for safety and efficacy in children. Growing concern for the prevalence of chronic disorders and increasing understanding of distinct phenotypes of these disorders points to a likely need for unique interventions matched to specific phenotypes. All contribute to the increasing complexity of ethical considerations in pediatric research.