Differences between vascular dementia and Alzheimer's dementia may be present in both risk factors and in behavioral manifestations. Behavioral distinctions may be apparent only at particular stages of the disease process, but comparisons at different stages require a large number of subjects. The California Alzheimer Disease Diagnostic and Treatment Center Program has collected data on a large number of subjects with dementia. We examined differences in risk factors and in behaviors in 502 subjects with vascular dementia and 810 subjects with probable Alzheimer's dementia. With respect to risk factors, vascular dementia subjects were more likely to have a history of general anesthesia. We found no difference in history of closed head trauma, family history of dementia, or cigarette smoking, suggesting that these factors are less likely to have a disease-specific etiologic role. With respect to behaviors, subjects with vascular dementia were more likely to have depression in all stages of dementia. Subjects with Alzheimer's dementia were more likely to exhibit wandering in the middle or late stages. Subjects were similar in five other behavioral factors in the three stages studied. We conclude that general anesthesia is a risk factor for vascular dementia and that depression is more prevalent in vascular dementia, while wandering is more characteristic of Alzheimer's dementia.