To evaluate observer bias and to estimate observer concordance for descriptions of personality changes in dementia, the authors examined the personality descriptions of dementia patients provided by 2 informants. Twenty-two patients with Alzheimer's disease were rated on the NEO–PI by each of 2 informants, the primary caregiver and another relative or friend. Each informant completed the NEO–PI to describe current behavior and premorbid behavior. Significant differences between premorbid and current descriptions were found for 4 of the 5 personality dimensions measured. There was substantial agreement between independent raters, as indicated by significant correlations between raters for 4 dimensions and the absence of significant differences between rater averages. These results suggest that both primary caregivers and others who know a patient well may serve as informants for studies of personality in dementia.