TAR-DNA-binding protein 43 (TDP-43) has been identified as a major component protein of ubiquitin-positive inclusions in brains from patients with frontotemporal lobar degeneration with ubiquitin-positive inclusions (FTLD-U) and amyotrophic lateral sclerosis. To obtain the precise prevalence of TDP-43 pathology in neurodegenerative disorders, we examined brains from patients with tauopathies and synucleinopathies as well as FTLD-U using immunohistochemical analysis. Consequently, TDP-43-positive inclusions within neurons and oligodendroglia were found in brains from patients with Alzheimer's disease (AD) and dementia with Lewy bodies (DLB) in addition to FTLD-U, but not with Parkinson's disease, Pick's disease, progressive supranuclear palsy, corticobasal degeneration or FTDP-17. The amygdala and hippocampus that were vulnerable to tau or alpha-synuclein pathology demonstrated more severe TDP-43 pathology in AD and DLB cases than in FTLD-U cases. In contrast, in the frontal cortex and basal ganglia that were vulnerable to TDP-43 pathology in FTLD-U, TDP-43 pathology was not observed in AD and DLB cases. Thus, the neuroanatomical distribution of TDP-43 pathology in AD and DLB cases was obviously different from that in FTLD-U cases. Furthermore, a subset of TDP-43-positive inclusions co-existed with neurofibrillary tangles (NFTs) or Lewy bodies (LBs) in the same neurons. Upon double-immunofluorescent labeling analysis, TDP-43 was hardly superimposed with tau, while TDP-43 was partially superimposed with alpha-synuclein, suggesting that neither NFTs nor LBs themselves show TDP-43 immunoreactivity and that TDP-43 pathology found in this study may be related in some way to AD and LB pathology. This study will provide a more in-depth understanding of the various pathogenic pathways leading to neurodegenerative disorders.