Fourteen case histories of persons who had a histological diagnosis of either senile dementia of the Alzheimer type, multiinfarct dementia, or a mixed dementia composed of these two types and who showed evidence of a moderate to severe dementia on psychological testing were rated for the presence of thirteen clinical features comprising Hachinski's Ischemic Score. These features are frequently considered primarily characteristic of vascular dementia. Persons with senile dementia of the Alzheimer type were clearly differentiable from persons with multiinfarct dementia and mixed dementia, while the latter two groups were indistinguishable from one another. In our sample, eight features were found to characterize those persons with vascular dementia. These data verify the usefulness of the Ischemic Score in differentiating between senile dementia of the Alzheimer type and vascular dementia.