Research into the clinical features of dementia has concentrated almost exclusively on the cognitive impairment. Perhaps this is not surprising, since deteriorating cognitive function is the most prominent feature, and a necessary one from the point of view of diagnosis (American Psychiatric Association, 1980; McKhann et al, 1984). However, this emphasis on cognitive function has led to the neglect of the other major feature of the disorder; namely, the changes in behaviour which have long been recognised. For example, Bleuler (1924), describing a sub-group of people with senile dementia, wrote that “the patients are always engaged in an apparent activity”. Some of the behavioural changes in dementia are a major source of distress for the carers of these patients (Argyle et al, 1985; Rabins et al, 1982; Gilleard et al, 1982) and often it is the disturbed behaviour which results both in patients coming to medical attention and in them requiring institutional care (Sanford, 1975; Chenoweth& Spencer, 1986). Frequently encountered examples include aggressive behaviour and ‘wandering’. The disturbed behaviour can take many other forms, including changes in eating, the hoarding and moving of objects, marked sleep disturbance, alterations in sexual behaviour, and incessant trailing behind people.