Clinical and morphologic findings from two patients with Progressive Supranuclear Palsy (PSP) are discussed and compared with observations in postencephalitic Parkinsonism. The most severely affected regions of the brain in PSP included the subthalamic, vestibular, and dentate nuclei in addition to those usually involved in postencephalitic Parkinsonism. Birefringent neurofibrillary tangles were found in degenerating neurons. Electron microscopy showed juxtaneuronal Hirano bodies, and electron-dense, membrane-bound, spheroid particles within degenerating neurons. The neurofibrillary tangles were composed of interlacing bundles of straight tubules in parallel array. In this respect the neurofibrillary tangles of PSP differ from those in postencephalitic Parkinsonism, which consist of “twisted tubules”, and from experimentally induced neurofibrillary tangles, which are composed of filaments.