Personality alterations in dementia of the Alzheimer type (DAT) are common but have received little systematic or quantitative investigation. In this study, changes in personality in patients with DAT were compared with those of nondemented retirees using a personality inventory. The inventory used information obtained from each subject's spouse. No personality changes were identified in the control subjects when pre- and post-retirement inventory scores were compared, whereas patients with DAT had highly significant alterations on 12 of the 18 inventory items. The results demonstrate that patients with DAT become more passive, more coarse, and less spontaneous as a result of the disease. Personality changes are a consistent part of the clinical syndrome of DAT and occur early in the course of the disease.