In recent years a number of patients suffering from long-standing postencephalitic parkinsonism have donated their brains to the United Kingdom Parkinson's Disease Society Brain Bank, in London. In view of the paucity of detailed neuropathological reports of the disease since the 1940s, we have carried out a clinicopathological study of eight recent cases. A spectrum of pathological change was seen, with highly variable involvement of cortical, subcortical and brainstem structures. There was no correlation between severity of disease and severity of pathology. The anatomical distribution of lesions was compared with that seen in progressive supranuclear palsy and Guamanian Parkinson-dementia complex. No definite histological features were identified that could distinguish any of the three disease entities. While the pathogenesis of postencephalitic parkinsonism, progressive supranuclear palsy and Guamanian Parkinson-dementia complex remains unknown, the presence of similar pathologies in these conditions suggests a common disease mechanism, despite the distinctive clinical features.