We performed a blinded study on 5 cases of hereditary diffuse leukoencephalopathy with spheroids and 10 cases of the pigmentary type of orthochromatic leukodystrophy, 6 of the latter having a family history of neurologic illness. Patients presented in the third to sixth decade with behavioral, cognitive, and motor symptoms. All cases displayed widespread myelin loss, predominantly frontotemporal with relative sparing of subcortical U-fibers, and variable numbers of both neuroaxonal spheroids and pigmented glia. Immunohistochemically, spheroids contained amyloid precursor/neurofilament proteins, several neurotransmitters or neuropeptides, and ubiquitin. Cytoplasmic inclusions in glia and numerous pigmented macrophages were autofluorescent and stained consistently with diastase-periodic acid-Schiff, prolonged Ziehl-Nielsen, and Sudan black, but the same cells labeled inconsistently for iron or ferritin. Ultrastructurally, the most characteristic autofluorescent glial lipopigments consisted of bosselated masses of granular, electron-dense material. These morphologic features are those of ceroid, an end-product of oxidative damage. Glial immunoreactivity for markers of oxidative stress (hemeoxygenase-1 and superoxide dismutase 2) and damage (4-hydroxynonenal, malondialdehyde, and nitrotyrosine) was noted, particularly in cases with increased iron and ferritin. These data support the hypothesis that the similar clinicopathologic features of hereditary diffuse leukoencephalopathy with spheroids and the pigmentary type of orthochromatic leukodystrophy reflect a common disease due, at least in part, to an oxidative insult.