P. C. Oliver

Background In an era of evidence‐based medicine, practice is constantly monitored for quality in accordance with the needs of clinical governance (Oyebode et al. 1999). This is likely to lead to a dramatic change in the treatment of those with intellectual disability (ID), in which evidence for effective intervention is limited for much that happens in ordinary practice. As Fraser (2000, p. 10) has commented, the word that best explains ‘the transformation of learning disability practice in the past 30 years is “enlightenment”.’ This is not enough to satisfy the demands of evidence, and Fraser exhorted us to embrace more research‐based practice in a subject that has previously escaped randomized controlled trials (RCTs) of treatment because of ethical concerns over capacity and consent, which constitute a denial of opportunity which ‘is now at last regarded as disenfranchising’.Conclusions The present paper describes the difficulties encountered in setting up a RCT of a common intervention, i.e. assertive community treatment, and concludes that a fundamental change in attitudes to health service research in ID is needed if proper evaluation is to prosper.