In this article, the authors illustrate a model of an effective ongoing and active collaboration among a group of pediatricians and child and adolescent psychiatrists. They demonstrate how regular meetings and active collaborative interventions broadened each other's understanding and treatment of children. The close relationship, trust, and understanding that developed as a result of this project had a marked impact on the treatment provided by both types of specialist. The concept of the developmentally informed pediatrician is the basic tenet of this project, which continues to have important implications for the training and practice of today's pediatricians.