We evaluated the presence and type of vascular lesions with computerized tomography (CT) in 94 cognitively impaired elderly patients who had been defined as degenerative (Alzheimer's disease, AD) or vascular (multi-infarct dementia, MID) dementia patients on the basis of clinical data. Twenty-six percent of the 77 AD, but only 59% of the 17 MID patients had vascular lesions. The most represented vascular lesions were leukoaraiosis in AD and hemispherical cortical lesions in MID patients. Age, signs indicative of, and risk factors for vascular disease were associated with vascular lesions on CT. We conclude that CT scan is a necessary complement to historical and clinical data in the detection of vascularity in demented patients.