The actual prevalence of child maltreatment is not clearly known, despite the importance of the problem. Using data from the National Child Abuse and Neglect Data System, Wildeman and colleagues seek to determine the proportion of children who are maltreated by 18 years of age. At 2011 rates, 1 in 8 children will experience maltreatment confirmed by child protections service workers by age 18 years. For black children, the risk is 1 in 5 and for Native American children, 1 in 7. Maltreatment is on the scale of other major public health problems that affect child health and well-being.