Background. Cross-sectional studies of non-cognitive symptoms in dementia show that patients with psychotic symptoms tend to have more disturbed behaviour. However, it is not known whether individuals who experience psychiatric symptoms early in dementia are more prone to develop behavioural problems later in the illness.

Method. The behaviour of 86 community-dwelling subjects with dementia was intensively studied for 4 years or until death, using an informant interview which was administered every 4 months on a median of eight occasions. The extent to which psychiatric symptoms, age, sex and cognitive function predicted clinically significant physical aggression or motor hyperactivity was assessed.

Results. Physical aggression was predicted by sad appearance and motor hyperactivity was predicted by persecutory ideas. These associations were robust, remaining significant over 2, 3 and 4 years of follow-up and were independent of cognitive function, age, sex and duration of illness.

Conclusions. There may be two distinct longitudinal syndromes of non-cognitive symptoms in dementia. This suggests that important aberrant behaviours in late dementia may share pathophysiological mechanisms with psychiatric symptoms in early dementia.