Background: Antipsychotics are perceived to be over-used in the management of behavioural problems in people with an intellectual disability (ID). Published guidelines have set good practice standards for the use of these drugs for behavioural indications. We sought to identify the range of indications for which antipsychotic drugs are prescribed in people with ID and to audit clinical practice against the standards. Method: Data were collected from the clinical records of individuals with ID who were under the care of mental health services in the UK, and prescribed an antipsychotic drug. Results: The sample comprised 2319 patients from 39 clinical services. Twenty-seven per cent of the patients had a diagnosis of a psychotic illness (ICD-10 F20-29) and 27% an affective illness (ICD-10 F30-39). The proportion who did not have a psychiatric diagnosis ranged from 6% of those with borderline/mild ID to 21% of those with severe/profound ID. Overall, the most common indications for prescribing an antipsychotic drug were comorbid psychotic illness, anxiety and agitation, and a range of behavioural disturbances. The prevalence of use of antipsychotic drugs to manage challenging behaviour in the absence of concomitant mental illness increased with the severity of ID and accounted for almost half of prescriptions in those with severe/profound ID. Adherence to the audit standards related to documentation of clinical indications and review of efficacy was high. Side effect monitoring was less assiduous. Conclusions: In clinical practice, most prescriptions for antipsychotic drugs in people with ID are consistent with the evidence base and the overall quality of prescribing practice, as measured against recognised standards, is good, although in some patients potentially remedial side effects may not be detected and treated.