Recent studies have shown that the dentate granular cells of the hippocampus are affected in patients with Alzheimer’s disease (AD). To gain a better understanding of the cytoskeletal alterations in these cells, we carried out immunocytochemical and immunoelectron microscopic analysis of the dentate gyrus of patients with primary degenerative dementias, using a monoclonal antibody against paired helical filaments (TG3). This antibody labeled a large number of spherical inclusions in the dentate granule cells of patients with AD and its Lewy body variant (LBV). These inclusions consisted of straight tubular structures (about 18–25 nm in diameter), similar to those found in progressive supranuclear palsy (PSP). These inclusions, although in a smaller number, were also found in demented patients with PSP, but not in those with diffuse Lewy body disease or age-matched controls. These findings indicate that the neurofibrillary alterations in the dentate granule cells of patients with AD, LBV and PSP share cytoskeletal similarities.