We studied the MRI and clinical factors associated with dementia following stroke by quantifying ventricle-to-brain ratio (VBR), anatomic region of infarction, and cortical, subcortical, and white matter areas of infarction in 24 stroke patients with dementia and 29 nondemented stroke patients. The factors that most strongly correlated with dementia were total white matter lesion (WML) area, left WML, VBR, right WML, age, left cortical infarction area, left parietal infarction area, and total infarction area. Using discriminant analysis, these factors correctly classified 28 of 29 nondemented patients and 18 of 24 demented patients. Both cortical and white matter total infarction area measurements were strongly associated with dementia in stroke patients, suggesting that these factors strongly influenced the development of dementia following stroke. There was a strong association between dementia and left- but not right-hemisphere infarction area. The only demographic factor that strongly associated with dementia was age.