This study investigated the ability of people with an intellectual disability to consent to psychological research. The criteria employed were based on the three elements of informed consent: information, competence and voluntariness. Participants were 40 people with an intellectual disability who had agreed to take part in a larger research study investigating their ability to consent to behavioural or medical treatment. A brief questionnaire consisting of six questions was administered to each participant to discover the extent of their ability to consent to take part in the larger study. A scoring protocol was developed to determine whether participants had answered each question satisfactorily. People appeared to understand the nature of the research, but had a limited understanding of the risks and benefits involved or of their right to refuse to participate or to drop out of the study. It is concluded that researchers must carefully assess the ability of people with an intellectual disability to consent before recruiting them to research studies and must be aware of the potential for this client group to agree to participate without fully understanding the implications.