Purpose - Antipsychotic drugs are frequently prescribed to people with intellectual disabilities (ID) to ameliorate psychotic symptoms and behavioural symptoms with and without mental condition. Guidelines recommend systematic evaluation of treatment effects and adverse effects, and limiting the treatment duration. Studies have shown that adherence to prescription guidelines is beneficial for clients' outcomes. Therefore, the purpose of this paper is to investigate the adherence to antipsychotic drug prescription guidelines in two treatment settings. Design/methodology/approach - A checklist, based on existing antipsychotic drug prescription guidelines, was used to evaluate the adherence of prescribers to guidelines in two settings in the Netherlands, i.e., in specialized intellectual disability (ID) care organizations and mental health care organizations. Data from medical records of clients who used antipsychotic drugs (n = 299) were compared to the items of the checklist. Findings - Treatment effects were measured with validated scales in both settings in only 2.7 per cent of cases. Prescriptions were for problem behaviour in the absence of a psychotic disorder or psychotic symptoms in 90 per cent (specialized ID care) and in 79 per cent (mental health care) of cases. In specialized ID care pipamperone (31.9 per cent) and in mental health care risperidone (48.5 per cent) was most often prescribed. Adverse effects were monitored more frequently in specialized ID care. Originality/value - The adherence to guidelines for prescribing antipsychotic drug to people with ID is insufficient in the Netherlands, because of shortcomings in the evaluation of treatment and adverse effects.