Background: The aim of the current study was to update an existing short measure of sexual knowledge and generate some initial reliability and normative data. Comparisons of sexual knowledge across several groups were made to examine whether or not a lack of sexual knowledge is related to sexual offending. Methods: The Bender Sexual Knowledge Questionnaire (BSKQ) was revised, and a new questionnaire, the General Sexual Knowledge Questionnaire (GSKQ), was created and administered to four groups of participants: (1) sex offenders with an intellectual disability (ID) and a history of engagement in treatment (n = 12); (2) sex offenders with an ID and no history of treatment (n = 13); (3) non-offenders with an ID (n = 28); and (4) non-offenders without an ID (n = 10). Between-group comparisons were made; internal consistency, split-half reliability and correlations were examined. Results: The internal consistency and the split-half reliability of the entire questionnaire was good. Non-offenders without an ID scored significantly higher than non-offenders with an ID on all sections of the GSKQ. Sex offenders who had undergone treatment scored significantly higher than non-offenders with an ID on several sections of this questionnaire. Conclusions: The initial findings from this study suggest that the psychometric properties of the GSKQ are promising. The assumption that lower sexual knowledge may be related to the risk of committing a sexual offence by people with IDs is possibly erroneous, and further research is required to clarify this possibility.