Few ill health situations are more degrading to people of any age than loss of reasoning, faculties, and personhood. These are the unpleasant consequences of delirium—a common condition affecting ill older people, particularly those with some degree of dementia. It is characterised by recent onset of fluctuating inattention and confusion, linked to one or more triggering factors. #### SUMMARY POINTS Delirium is a major burden to healthcare services and has been largely ignored by health service planners and practitioners.1 Moreover, healthcare systems and services often unintentionally stimulate or substantially aggravate the development of delirium in older people.2 This might be understandable if delirium was unavoidable or untreatable, but the existing evidence base for delirium is sufficiently robust for prevention or attenuation of the condition to be a realistic proposition. There is a pressing need to take this action because the outcomes for delirium are poor: it contributes to substantial morbidity and mortality, causes considerable distress to patients and families, and is expensive—an estimated additional $2500 (£1275; €1875) per patient (a $6.9bn annual expenditure for Medicare in 2004).3 We searched Medline and the Cochrane Library from 1996 to 2006. We drew additional material from our personal libraries of delirium references, focusing particularly on systematic reviews. Delirium is an important problem for all clinical services providing care for older people, particularly emergency departments; general medical, elderly care, surgical, and …