In this article, we present an update on epidemiologic research that addresses the scope and impact of children's exposure to traumatic events in daily living, as well as under special circumstances, such as natural disasters. Toward this end, we provide an overview of the findings of key selected studies that estimate the prevalence of children's exposure to trauma and associated developmental, functional, mental, and physical health problems. Over the past few years, epidemiologic research on child traumatic stress has demonstrated that children's exposure to traumatic events is more common than once thought and that children exposed to multiple traumatic events are at a substantially greater risk for a wide range of adverse mental and physical health problems than children who have not suffered cumulative traumatic experiences. These findings have important implications for the provision of mental health and medical services to children and adolescents who have experienced child traumatic stress.