A cerebral ganglioglioma contained abundant neurofibrillary tangles (NFTs) of the paired helical filament (PHF) type. The NFTs in the tumor were argyrophilic and Congo red and thioflavin-S positive. Immunohistochemically, the NFTs were reactive with antibodies to phosphorylated neurofilament protein, PHF/tau and ubiquitin. The demonstration in the neoplasm of abnormally phosphorylated and ubiquitinated cytoskeletal components, similar in morphology and in immunoreactivity to those seen in NFTs of Alzheimer's disease, suggest that similar pathogenetic mechanisms may operate in both conditions.