This retrospective review of medical records was designed to address three questions: 1) Can the depression seen in some patients with Dementia of the Alzheimer's Type (DAT) be successfully treated? 2) Does this treatment lead to any long-term improvement in the patient's cognitive status? and 3) Do patients with coexisting DAT and depression have a different long-term clinical course than nondepressed DAT patients? In the authors' sample of 131 DAT subjects, 41 (31%) also met DMS-III criteria for a major affective disorder. Of those DAT plus depression patients whose records reflected treatment (usually with a tricyclic antidepressant), 85% (17 of 20) showed clear evidence of improvement in mood, vegetative signs, or activities of daily living (ADLs) based on review of the medical record. An analysis of change in cognitive function (measured by the Folstein Mini-Mental State) and five global measures failed to reveal any differences between the depressed and nondepressed groups after a mean interval of 17 months. The depression that occurs in approximately one-quarter to one-third of DAT patients appears to respond to appropriate therapy. These patients often show improvement in their mood and ADLs but remain demented.