Antipsychotic medication is the standard treatment for people with learning disability and schizophrenia.To determine the efficacy of any antipsychotic medication for treating people with a dual diagnosis of learning disability and schizophrenia.Electronic searching of Biological Abstracts, the Cochrane Schizophrenia Group's Register of trials (September 2000), the Cochrane Library, EMBASE, PsycLIT MEDLINE and National Research Register (Issue 3 2000). Unpublished data were sought from pharmaceutical companies. Both authors independently selected the relevant studies from the reports identified in this way.1. All randomised controlled trials of antipsychotic medication, regardless of dosage, versus a placebo control, of longer than one month's duration. 2. Anyone over 18 years of age with both learning disability and schizophrenia. Learning disability was defined as a measured IQ of 70 or less. Any mode of diagnosis of schizophrenia was acceptable.The two reviewers independently attempted to select and then extract data but it was not possible to do this with the single study that met the inclusion criteria.Only one relevant randomised trial was found by the searches. This study included four people with a dual diagnosis of schizophrenia and learning disability, but results were available for only two. The groups to which the other two people were allocated were unclear. In order to display the data, too many assumptions would have to have been made about these other two people and any results would be uninformative and potentially misleading.Using the methods described the reviewers found no randomised controlled trial evidence to guide the use of antipsychotic medication for those with both learning disability and schizophrenia. Until the urgent need for randomised controlled trials is met, clinical practice will continue to be guided by extrapolation of evidence from randomised controlled trials involving people with schizophrenia but without learning disability and non-randomised trials of those with learning disability and schizophrenia.