There are not many studies on the use of clozapine in patients with intellectual disability (ID). The authors describe a case series of patients treated with clozapine, drawn from a medium secure unit, a low secure assessment and treatment service and a community team in the London region. A retrospective file-review of patients treated in these three settings during the time period March-June 2002 was performed (n=24). Information was collected using a semistructured proforma. Of the 24 patients, 67% had schizophrenia, 17% had schizoaffective disorder and 8% had bipolar disorder. Patients had been unwell for a mean of 6 years and had been tried on a mean of four antipsychotics. The mean maximum dose of clozapine was 488mg. The outcomes on the clinical global impression (CGI) scale showed 29% very much improved, 42% much improved, 21% minimally improved and 8% no change. 54% of the whole sample and 53% of those from the medium secure unit were discharged to homes in the community. The drug had to be stopped in four patients, of which three were because of neutropaenia. Clozapine appears to be safe and efficacious in many people with ID. Careful monitoring of side-effects is needed during therapy.