Although sleep problems often comprise core features of psychiatric disorders, inadequate attention has been paid to the complex, reciprocal relationships involved in the early regulation of sleep, emotion, and behavior. In this paper, we review the pediatric literature examining sleep in children with primary psychiatric disorders as well as evidence for the role of early sleep problems as a risk factor for the development of psychopathology. Based on these cumulative data, possible mechanisms and implications of early sleep disruption are considered. Finally, assessment recommendations for mental health clinicians working with children and adolescents are provided toward reducing the risk of and improving treatments for sleep disorders and psychopathology in children and adolescents.