Leuko-araiosis is a purely descriptive term indicating images of bilateral, patchy or diffuse areas of decreased density frequently observable in the deep white matter on brain CT scans of adults and elderly subjects. While in earlier studies these images were considered as the "in vivo" expression of leukoencephalopathy associated with Binswanger disease, subsequently they have been reported in a rather broad spectrum of clinical conditions, including healthy aging and dementia of different types. Evidence of arterial hypertension and lacunar stroke is found in only two-thirds of subjects with leuko-araiosis. The results of pathological studies are conflicting about the nature of leukoencephalopathy, and the type and severity of medullary artery involvements. Probably several mechanisms underlie leuko-araiosis. They might act separately or be combined in different cases. Classification by physiopathological mechanism may be a suitable aim of future research in this field.