Background: People with intellectual disabilities can be exposed to sexual abuse and they can display harmful sexual behaviour. This study aimed to identify barriers to preventing harmful sexual behaviour in people with intellectual disabilities within the support sector and the justice system. Method: We conducted focus group interviews with 20 participants from hospital-based habilitation centres, community residences, schools and the criminal justice system. Results: The interviews identified a lack of education and guidelines for stakeholders or carers on regulating the sexual behaviour of people with intellectual disabilities. The criminal justice system faces challenges related to prioritising, understanding and communicating. People with intellectual disabilities may lack an understanding of the concepts of sexual consent and acceptable sexual behaviour. Conclusion: There is a need to improve knowledge about intellectual disability and how to prevent harmful sexual behaviour for professional caregivers in the support sector and the criminal justice system.