Published studies of forensic child sexual abuse (CSA) evaluations by mental health and medical professionals and paraprofessionals (MHPs) were analysed in order to evaluate two widely held assumptions. These related assumptions are (1) evidence that corroborates children's reports of sexual abuse is rare in forensic CSA evaluations; and (2) in the vast majority of evaluations, MHPs base their judgements about whether or not sexual abuse allegations are true on their assessments of children's reports of sexual abuse and other psychosocial data. Data from five chart review studies of a combined total of 894 forensic CSA evaluations provided sufficient information to assess the validity of these assumptions. Corroborative evidence was present in 36% of the 894 evaluations and in 54% of evaluations in which MHPs judged the allegations likely to be true, contradicting the first assumption. In the evaluations in which corroborative evidence was present, the presence or absence of a child's report of sexual abuse was only weakly associated with MHPs' judgements about the validity of the allegations (allegations in almost all corroborated cases were judged likely to be true, even in the absence of a child's report), partially contradicting the second assumption. Implications of this analysis for research and policy are discussed. Copyright © 2010 John Wiley & Sons, Ltd.