The Optimus study in South Africa was designed specifically to estimate the annual incidence and lifetime prevalence of child sexual abuse and maltreatment in South Africa. Prior to this study, no nationally representative data on the extent or impact of child sexual abuse existed. In order to obtain a comprehensive picture of the nature, extent and impact of child sexual abuse in the country, the study drew on two data sources. The first was a population study conducted with a sample of 15 to 17 year old adolescents recruited nationally from schools (n=4086) as well as households (n=5631), while the second was an agency component that consisted of a series of in-depth interviews and focus group discussions with front-line staff and child protection agency directors servicing the communities or geographical spaces identified through the population survey sampling process. Through a thorough exploration of these areas, the study identifies where resources can best be targeted, provides a local evidence base for the development of effective interventions, and identifies whether intervening in one form of abuse or neglect might also have the potential to address other forms of violence.