The fine structure of the hypertrophic olive is reported in a case of progressive supranuclear palsy, the cause of which would be attributed to extensive symmetrical lesions in the dentate nuclei of the cerebellum and central tegmental tracts of the pons. Ultrastructurally, the enlarged neurons and their processes showed massive aggregations of neurofilaments, large accumulations of concentric laminated bodies, and occasional abnormal neurofibers (paired helical filaments and straight tubules). Their implications are briefly discussed in relation to olivary hypertrophy. Eosinophilic globules were seen in a neuron. Glomeruloid bodies were not seen.