Although cognitive impairment is the predominant feature of dementia, personality changes are also frequently reported. This study aimed to describe the nature of personality change in dementia of the Alzheimer type (DAT) and the relationship of this change to cognitive decline. An informant-based instrument was developed based on a personality inventory designed by Lewis Goldberg for measuring personality in the normal population. Twentyeight clinicians used this inventory to rate the difference between people suffering from DAT and normal elderly people. Differences were found in all five factors of personality, with Conscientiousness and Intellect showing the most difference and Agreeableness showing the least difference. Based on the findings of this first study, a smaller questionnaire of 46 traits was developed. This was completed by 50 relatives of DAT patients, 50 relatives of controls and 167 carers of dementia sufferers recruited from Alzheimer's Association support groups. Principal components analysis revealed a large factor which accounted for 33% of the variance suggesting a global change in personality. Rotation revealed three meaningful factors. Two of these factors were highly correlated to cognitive decline while the third showed only a moderate correlation. The significance of these results is discussed. KEYwoRDs-personality change; dementia of the Alzheimer type; cognitive decline