A histopathological study was carried out on the brains of eight ex-boxers (ages 56 to 83) using conventional histological staining methods and immunocytochemistry with antibodies to amyloid beta-protein and the PHF-related tau protein. All cases showed a large number of tau-immunoreactive neurofibrillary tangles and also beta-protein immunoreactive senile plaques in the cortex. In the areas with many neurofibrillary tangles, neuropil threads with tau-immunoreactivity were also observed, and some of the senile plaque lesions were surrounded by abnormal neurites with tau-immunoreactivity. Moreover, three cases revealed beta-protein-type cerebrovascular amyloid deposits on both leptomeningeal and cortical blood vessels. The present observations indicate that the cerebral pathology of dementia pugilistica is very similar to that of Alzheimer's disease and suggest that these two disorders share some common etiological and pathogenic mechanisms.