This chapter describes the prevalence of early childhood trauma in the general population of the USA using data from the National Comorbidity Study-Replication (NCS-R). It discusses some of the methodological issues around assessing the prevalence of childhood trauma, focusing on estimates of child maltreatment as a specific example. The chapter explains the risk factors for childhood trauma. The prevalence of exposure to any traumatic event, to any other injury or shocking experience and for most specific event types did not significantly differ by race. Factors associated with greater risk of childhood trauma occur at the individual, family, neighborhood, local, regional and national level; the bulk of research focuses on individual and family factors. Individual factors associated with risk of childhood trauma include demographic descriptors such as sex, age and race/ethnicity, as well as health and behavioral characteristics, including mental health, substance use, sexuality and prior traumatization.