Background: Various explanations of sexual offending in men with intellectual disability (ID) have stressed sexual deviance and a lack of developmental socio-sexual knowledge. Method: Using the normative dataset of people with ID from the development of the "Socio-Sexual Knowledge and Attitudes Assessment Tool--Revised" (SSKAAT-R: Griffiths & Lunsky, 2003), two samples of individuals with ID and a history of sexual offence were compared on sexual knowledge to matched samples of individuals with ID and no known sexual offences. Results: Offenders with ID who were identified as having engaged in sexually inappropriate behaviour, such as public masturbation or touching someone inappropriately, did not differ in terms of sexual knowledge from their matched sample of individuals with ID with no sexual offence history, whereas offenders who had committed more serious offences demonstrated greater sexual knowledge than matched non-offenders. When only those individuals who had received prior sex education were compared in terms of sexual knowledge, there were no differences between groups. However, sex offenders (serious offences) expressed more liberal attitudes than sex offenders (inappropriate behaviour) and non-offenders towards same-sex activities. Conclusions: The study points to the dynamic effect of socio-sexual education on offenders' knowledge and attitudes, and highlights potential differences in the knowledge and attitudes of different subtypes of offenders. (Contains 2 tables and 1 figure.)