The psychiatric assessment of young children is a multifaceted endeavor, and developmental assessment, formal or informal, is an integral component. Sound developmental assessment, however, is a thoughtful process that requires specialized knowledge of young children, appropriate assessment methods, and the interpretation and integration of psychiatric and developmental data. The art and science of developmental assessment have improved significantly over the past century. Despite technologic advances in instruments, clinicians must be as astute and mindful as ever of what constitutes sound diagnostic formulation and treatment planning. Although many limitations and potential abuses certainly exist, results of developmental evaluations play a unique and often essential role in the comprehensive psychiatric assessment of young children.