While the occurrence ofposttraumatic stress disorders (PTSD) in children and adolescents is undoubted, knowledge about the disorder in infants and toddlers is scarce. The lack of an accurate research base is mainly due to challenges in assessing PTSD in infants and toddlers. The development of an alternative set of diagnostic criteria, its empirical testing and the design of an examiner-based interview are recent and important steps. This article reviews the literature on PTSD in infants and toddlers. It defines the disorder and emphasizes its distinctive features in this age group. Demonstrating the development of an alternative set of diagnostic criteria and overviewing the existing assessment tools are central issues. A German version of the Posttraumatic Stress Disorder Semi-Structured Interview and Observational Record for Infants and Young Children (Scheeringa u. Zeanah, 2005) is presented for the first time. The state of research in prevalence and therapy of PTSD in infants and toddlers is described and recommendations for research and clinical practice are provided.