Our purpose was to investigate leukoaraïosis (LA) using three-dimensional MR imaging combined with advanced image-processing technology to attempt to group signal abnormalities according to their etiology. Coronal T2-weighted fast fluid-attenuated inversion-recovery (FLAIR) sequences and three-dimensional T1-weighted fast spoiled gradient recalled echo sequences were used to examine cerebral white matter changes in 75 elderly people with memory complaint but no dementia. They were otherwise healthy, community-dwelling subjects. Three subtypes of LA were defined on the basis of their shape, geography and extent: the so-called subependymal/subpial LA, perivascular LA and "bands" along long white matter tracts. Subependymal changes were directly contiguous with ventricular spaces. They showed features of "water hammer" lesions with ventricular systematisation and a more frequent location around the frontal horns than around the bodies (P=.0008). The use of cerebrospinal fluid (CSF) contiguity criterion allowed a classification of splenial changes in the subpial group. Conversely, posterior periventricular lesions in the centrum ovale as well as irregular and extensive periventricular lesions were not directly contiguous with CSF spaces. The so-called perivascular changes showed features of small-vessel-associated disease; they surrounded linear CSF-like signals that followed the direction of perforating vessels. Distribution of these perivascular changes appeared heterogeneous (P ranging from .04 to 5.10(-16)). These findings suggest that subependymal/subpial LA and subcortical LA may be separate manifestations of a single underlying pulse-wave encephalopathy.