Several authors have suggested that lack of sexual knowledge is a primary reason for inappropriate sexual behaviour in men with intellectual disabilities. This hypothesis, counterfeit deviance, is tested in the current report with two separate cohorts comparing sex offenders and controls, both with intellectual disability. The Socio-Sexual Knowledge and Attitudes Test was completed on all participants and any significant differences between groups indicated that the sex offender cohort had a higher level of knowledge. The hypothesis has not been supported. In addition, a positive relationship was found between intellectual ability and knowledge for the control cohort but not for the sex offender cohort.