Background. For people with intellectual disabilities there is a difficult balance to be struck between empowering people to claim their sexual rights and protecting them from abuse. Hypothetically, services should be guided by whether a particular person with intellectual disabilities has the capacity to consent to sexual relationships. However, there has been little agreement on how to define such capacity. This study examines the issue of capacity to consent to sexual relationships using a functional approach.

Method. Adults with intellectual disabilities (n=60) and young people presumed in law able to consent (n=60) were assessed for their sexual knowledge and vulnerability to abuse.

Results. Adults with intellectual disabilities were significantly less knowledgeable about almost all aspects of sex and appeared significantly more vulnerable to abuse, having difficulty at times distinguishing abusive from consenting relationships. Nevertheless, some adults with intellectual disabilities scored highly on all measures, especially if they had relatively high IQs and had had sex education.

Conclusions. The reasons for the poorer knowledge and increased vulnerability of people with intellectual disabilities are discussed and it is recommended that they should have on-going access to sex education. Implications of the findings for definitions of capacity to consent to sexual relationships are considered.