The paper reviews several psychobiological systems with regard to their functioning under normal stress and in the presence of posttraumatic stress disorder, with a focus on research findings in children and adolescents, and the implications of these findings for clinical intervention for traumatized children. Research regarding the neurobiology of posttraumatic stress disorder provides growing evidence of the negative impact of traumatic events on childhood brain development and functioning. The article emphasizes the importance of early identification and treatment of traumatized children. It recommends more research testing potential treatments, particularly pharmacologic therapies, alone and in combination, for children with a variety of trauma-related symptoms. It also recommends additional efforts to provide training in those interventions that have demonstrated effectiveness. References, bibliography