Patients with neurodegenerative disease show distinct patterns of personality change, some of which may be traced to focal neurological damage, whereas others may be mediated by cultural reactions to functional impairment. Although such changes are early and pervasive in behavioral variant frontotemporal dementia (bvFTD), and milder changes are seen in Alzheimer disease (AD), no study has examined all Big 5 factors of personality in mild cognitive impairment (MCI) patients. In addition, the influence of culture and ethnicity on disease-related personality changes has seldom been examined. Premorbid and current personality were measured in 47 Greek patients with bvFTD, AD, and MCI on the basis of informant reports using the Traits Personality Questionnaire 5, a 5-factor inventory in the Greek language that accounts for Greek cultural factors. bvFTDs showed greater decreases in conscientiousness compared with ADs and MCIs. ADs and MCIs showed increased neuroticism, whereas the bvFTD patients were rated as having become much less neurotic in the course of their disease. The pattern of personality change in MCIs was very similar to that of ADs, supporting recent evidence that personality changes occur as early as the MCI disease stage. In all the groups, personality changes were similar to those previously described in non-Mediterranean cultures, supporting the hypothesis that they may result directly from disease-specific neurological processes.