Disease-specific findings in the substantia nigra were examined in cases of progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), and parkinsonism-dementia complex of Guam (PDC); diseases in which the patients exhibit dementia and parkinsonism, with neurofibrillary tangles (NFTs) and glial tangles composed of hyperphosphorylated tau. Loss of pigmented neurons was extremely severe in these 3 diseases, and decrease of the nonpigmented neurons was severe in PSP and CBD. On the other hand, in PDC the decrease of the nonpigmented neurons was different in each patient. Topographically, in PSP the nonpigmented neurons were particularly depleted in the ventral part and relative preservation of the pigmented neurons was observed in the medial part at the level examined. Many NFTs were observed in PDC. Although the number of NFTs was small, many pretangles were seen in the neurons in CBD. Granular and hazy astrocytic inclusions were identified exclusively in PDC. Numerous argyrophilic neuropile threads were identified in CBD and PSP, but these were few in PDC. Many foamy spheroid bodies as well as coiled bodies were observed in PSP and CBD, but only a few were observed in PDC. In conclusion, PDC is a disease that is distinctly different from PSP and CBD. It is possible to differentiate between PSP and CBD by the occurrence of many pretangles in CBD, but some similarities between these 2 diseases indicate the existence of common pathological mechanisms.