Many older people living in residential care have significant cognitive impairment. It has been estimated that the prevalence of dementia in English nursing-home residents is approximately 70% (MacDonald et al. 2002) and that the prevalence of delirium among elderly hospitalised patients is between 10% and 60% (Fick, Agostini & Inouye 2002). Delirium is thought to be unrecognised in 32–66% of patients, and delirium superimposed on dementia has been reported as occurring in 22–89% of hospitalised and community populations (Fick, Agostini & Inouye 2002).