Despite the prevalence of childhood trauma, there are currently no developmentally oriented cognitive theories of posttraumatic stress disorder (PTSD). This paper outlines the definitional issues of PTSD in children, reviews the incidence of PTSD in children, and compares PTSD profiles in children and adults. We propose that a cognitive theory of childhood PTSD needs to accommodate developmental factors, including knowledge, language development, memory, emotion regulation, and social cognition, in addition to contextual factors such as family interactions. Implications of these developmental factors for assessment and treatment of traumatized children are discussed.