Patients with clinical diagnoses of Alzheimer's disease, vascular dementia, or undifferentiated dementia were rated on standardized measures of depression, cognitive impairment, and functional impairment. Logistic regression was used to evaluate the relationship between functional or cognitive impairment, as well as their interaction, and depressive features in each group. This analysis revealed notable differences by type of dementia. The results imply that the mechanisms underlying depression in Alzheimer's disease may be different from those in vascular and other types of dementia. These results also provide indicators to the clinician for further evaluation of depression in different dementia subtypes.