OBJECTIVES: To determine the prevalence and quality of antipsychotic prescribing for people with intellectual disability (ID). DESIGN: A clinical audit of prescribing practice in the context of a quality improvement programme. Practice standards for audit were derived from relevant, evidence-based guidelines, including NICE. Data were mainly collected from the clinical records, but to determine the clinical rationale for using antipsychotic medication in individual cases, prescribers could also be directly questioned. SETTINGS: 54 mental health services in the UK, which were predominantly NHS Trusts. PARTICIPANTS: Information on prescribing was collected for 5654 people with ID. RESULTS: Almost two-thirds (64%) of the total sample was prescribed antipsychotic medication, of whom almost half (49%) had a schizophrenia spectrum or affective disorder diagnosis, while a further third (36%) exhibited behaviours recognised by NICE as potentially legitimate targets for such treatment such as violence, aggression or self-injury. With respect to screening for potential side effects within the past year, 41% had a documented measure of body weight (range across participating services 18-100%), 32% blood pressure (0-100%) and 37% blood glucose and blood lipids (0-100%). CONCLUSIONS: These data from mental health services across the UK suggest that antipsychotic medications are not widely used outside of licensed and/or evidence-based indications in people with ID. However, screening for side effects in those patients on continuing antipsychotic medication was inconsistent across the participating services and the possibility that a small number of these services failed to meet basic standards of care cannot be excluded.