There is a significant gap in understanding the risk of sexual victimization in individuals with autism spectrum disorders (ASD) and the variables that contribute to risk. Age appropriate sexual interest, limited sexual knowledge and experiences, and social deficits, may place adults with ASD at increased risk. Ninety-five adults with ASD and 117 adults without ASD completed questionnaires regarding sexual knowledge sources, actual knowledge, perceived knowledge, and sexual victimization. Individuals with ASD obtained less of their sexual knowledge from social sources, more sexual knowledge from non-social sources, had less perceived and actual knowledge, and experienced more sexual victimization than controls. The increased risk of victimization by individuals with ASD was partially mediated by their actual knowledge. The link between knowledge and victimization has important clinical implications for interventions.