This paper analyses the histopathological characteristics and the topographical distribution of 'pure' HIV-associated white matter lesions of the brain in 18 AIDS patients at autopsy; it includes a time-controlled correlation of neuropathology to clinical staging of the AIDS dementia complex. Three distinct lesion types can be delineated: 1 Vacuolar myelin damage (n = 15) in the hemispheric and interhemispheric white matter, in projection fibre tracts, and in intracerebral segments of cranial nerves III, VII, and VIII; 2 Angiocentric foci (n = 14), disseminated randomly in the white matter; 3 HIV leukoencephalopathy (n = 14), as previously defined, seen predominantly in the hemispheric white matter. As a sole lesion type, HIV leukoencephalopathy is found in two cases, while vacuolar myelin damage and angiocentric foci always occur in combination with one or both other types of pathology. Patients with advanced AIDS-dementia complex consistently show severe and combined white matter pathologies at autopsy. We conclude that, in addition to the previously defined features of diffuse HIV leukoencephalopathy, vacuolar myelin damage and angiocentric foci are significant and frequent components of white matter pathology in AIDS autopsies. This reflects the multitude of pathogenetic factors which co-operate in damaging the brain in AIDS. The advanced AIDS dementia complex correlates with the combined and severe white matter lesions.