The frequency of symptoms of depression (Feighner criteria) was evaluated in subjects with dementia of the Alzheimer type (DAT) and matched controls enrolled in a longitudinal natural history study of DAT. Despite enrollment criteria which excluded subjects with affective disorders, the collateral sources of subjects with DAT described these subjects as having significantly more "depressive" symptoms than controls without dementia at entry, and at 15- and 34-month follow-up. The collateral sources of the subjects with DAT reported that these demented individuals experienced significantly greater loss of interest, decreased energy, difficulty in thinking and concentrating, and psychomotor agitation or retardation then did the control group. The subjects with DAT reported fewer symptoms than did their collateral sources, but like their collateral sources, they did not report a global elevation of all Feighner symptoms, but rather related significantly greater difficulty in thinking and concentrating than the controls and a tendency toward loss of interest and psychomotor changes. No subject became clinically depressed. The results suggest a significant overlap between the symptoms of dementia and depression. The frequency with which the above symptoms occur in DAT confounds the use of Feighner and, by extension, DSM-III criteria in diagnosing depression in cognitively impaired individuals with DAT.