Computed tomography and magnetic resonance imaging in the elderly have demonstrated the common occurrence of deep white-matter lesions in the aging brain. These radiologic lesions (leukoaraiosis) may represent an early marker of dementia. At autopsy, an ischemic periventricular leukoencephalopathy (Binswanger's disease) has been found in most cases. The clinical spectrum of Binswanger's disease appears to range from asymptomatic radiologic lesions to dementia with focal deficits, frontal signs, pseudobulbar palsy, gait difficulties, and urinary incontinence. The name senile dementia of the Binswanger type (SDBT) is proposed for this poorly recognized, vascular form of subcortical dementia. The SDBT probably results from cortical disconnection most likely caused by hypoperfusion. In contrast, multi-infarct dementia is correlated with multiple large and small strokes that cause a loss of over 50 to 100 mL of brain volume. The periventricular white matter is a watershed area irrigated by long, penetrating medullary arteries. Risk factors for SDBT are small-artery diseases, such as hypertension and amyloid angiopathy, impaired autoregulation of cerebral blood flow in the elderly, and periventricular hypoperfusion due to cardiac failure, arrhythmias, and hypotension. The SDBT may be a potentially preventable and treatable form of dementia.