Among 251 patients examined 3 months after the onset of acute ischemic stroke, we diagnosed dementia in 66 (26.3%) by using modified DSM-III-R criteria based on neuropsychological, neurological, functional, and psychiatric examinations. We used a logistic regression model to derive odds ratios (ORs) for clinical factors independently related to dementia in this cross-sectional sample. Dementia was significantly associated with age, education, and race. A history of prior stroke (OR = 2.7) and diabetes mellitus (OR = 2.6) was also independently related to dementia, but hypertension and cardiac disease were not. Stroke features associated with dementia included lacunar infarction compared with all other subtypes combined (OR = 2.7) and hemispheric laterality in relation to brainstem or cerebellar location. There was a predominance of dementia in patients with left-sided lesions (OR = 4.7), an effect not explained by aphasia. Dementia was especially common with infarctions in the left posterior cerebral and anterior cerebral artery territories. A major dominant hemispheral syndrome (reflecting size and laterality) was also independently associated with dementia (OR = 3.9). We suggest that dementia after ischemic stroke is a result of multiple independent factors, including both small subcortical and large cortical infarcts especially involving the left medial frontal and temporal regions, with additional contributions by demographic and vascular risk factors.