Background: Five factors are proposed as important in influencing the provision of psychological therapy to people with intellectual disabilities (IDs): the perceived effectiveness of psychological therapy, individual clinician competence, service resources (number of trained clinicians), the level of the clients disability and the diagnostic overshadowing bias. Method: A prospective questionnaire design was used. A survey style questionnaire was sent out to clinical psychologists (n = 412) and psychiatrists (n = 274) working in ID services in the UK. Responses were received from 133 psychologists and 90 psychiatrists. Results: Perceived competence, the level of the clients disability and the diagnostic overshadowing bias all appeared to be important factors. The perceived effectiveness of psychological therapy with this client group and service resources appeared less important than hypothesized. Conclusion: Whereas the debates in research publications tend to focus on broad issues of effectiveness, clinicians themselves appear more concerned with their personal skill levels. The issue of the appropriateness of psychological therapies for people with more severe levels of disability remains largely unresearched.