We recently described a family with chromosome 17-linked dementia, characterized clinically by disinhibition-dementia-parkinsonism-amyotrophy complex. We report now the neuropathology of 6 affected family members. This included semiquantitative scoring of neuronal loss, gliosis, and spongiosis and immunocytochemical and ultrastructural characterization of neuronal and glial inclusions. The changes consisted of circumscribed neuronal loss, gliosis, and spongiosis of limbic neocortical areas and frontal, temporal, and occipital association areas. Similar changes were present in subcortical nuclei, most severe in the substantia nigra, but also involved the ventral striatum and amygdala. The hippocampus was spared except for degeneration of the afferent perforant tract, secondary to entorhinal nerve cell loss, Argyrophilic neuronal inclusions, with a characteristic immunocytochemical profile, were found in brainstem nuclei, hypothalamus, and basal ganglia. Ultrastructurally, in 3 patients these inclusions showed hitherto undescribed abnormally assembled filaments. Glial cytoplasmic inclusions were widespread in white matter structures. Immunocytochemistry failed to demonstrate the protease-resistant prion protein. The pathology appears to be unique, involving various cortical and subcortical structures, and is consistent with the clinical findings of Kluver-Bucy-like syndrome, parkinsonism, and frontal lobe dementia. For this entity we suggest the term ''chromosome 17-linked dementia.''