A 56-year-old woman with Werner's syndrome was admitted to our hospital because of intractable foot ulcer and malnutrition. She presented dementia consisting of childish behaviour, loss of intelligence, and severe amnesia. Brain CT revealed diffuse periventricular low density areas, and brain MRI also disclosed periventricular high intensity areas under T2-intensified conditions. These findings gave a diagnosis of progressive subcortical vascular encephalopathy of the Binswanger type, which seemed to be the cause of her dementia. She finally died of heart failure due to acute myocardial infarction. Mild to moderate demyelinization was found in the subcortical area of the autopsied cerebrum, confirming the clinical diagnosis. Generalized atherosclerosis characteristic of Werner's syndrome may have predisposed this patient to Binswanger's encephalopathy.