BACKGROUND Depressive symptoms are frequent complications of Alzheimer's disease (AD). We hypothesized that AD patients with depression would be more likely than nondepressed AD patients to show deep white-matter, subcortical gray-matter, and periventricular hyperintensities on magnetic resonance imaging (MRI). METHODS In a retrospective study of 31 AD patients, depression was characterized by clinical diagnosis (DSM-III-R major depression, depressive symptoms, or no depression), a clinician-rated depression scale, and informant ratings of premorbid (before memory disorder) as well as current depression using the NEO Personality Inventory (NEO-PI), and related to qualitative and quantitative ratings of MRI hyperintensities. RESULTS In contrast to reports in nondemented elderly patients, there was no relationship between clinical diagnosis of major depressive episode and hyperintensities; however, clinician-rated depressive symptoms were higher in subjects with large anterior hyperintensities. In the early-onset AD group only, MRI abnormalities were related to greater premorbid depression, and less increase in depression after the onset of dementia, as rated by informants on the NEO-PI. CONCLUSIONS Results highlight the need to consider early- and late-onset AD separately when assessing relationships between personality and MRI abnormalities, and to consider premorbid personality style when drawing conclusions about the etiology of depressive features seen in AD.