How personality changes in Alzheimer's disease is not well understood. Accentuations of premorbid personality, systematic shifts in personality traits, and specific personality changes affecting subtypes of patients have been postulated. To investigate which of these alternatives occurs in Alzheimer's disease, caregivers were given a comprehensive personality inventory standardized for use by informants. Caregivers observed more neurotic, less extroverted, and less conscientious behavior. To a smaller extent, patients with Alzheimer's disease were reported as becoming less agreeable and less open. The changes in reports of neuroticism, extroversion, agreeableness, and openness suggested consistent systematic shifts across all patients. Patients with depressive features were reported to have been more neurotic; those with paranoid delusions were reported as having been more hostile. Premorbid personality traits may predispose to subsequent psychiatric symptoms in Alzheimer's disease.