The focus of this chapter is to examine how the conceptual differences influence the definition and prevalence of sexual abuse among children, adolescence and adults. Attempting to understand measures, sources of data and special groups influences on prevalence rates is a challenge. It was observed that the prevalence of sexual abuse varies according to the type of concept and definitions, legal criteria, method of data collection, like interview methods, questionnaires, or self reports, and the source of data such as general population or specific groups such as prisoners, and individuals with disabilities are used for the study. In some studies, the rates are exaggerated because of the definitions. The chapter concludes that is important to evaluate prevalence studies of sexual abuse on different dimensions and criteria to make final conclusions.