A hamartomatous gangliocytoma was observed in the hypothalamus of a 54-year-old woman. The ganglion cells were atypical, highly pleomorphic and often multinucleated, and they possessed neurofibrillary changes, granulovacuolar degeneration, and argentophilic bodies. The neuronal changes were highly selective and were not found in other parts of the brain. The tumor was also characterized by the presence of angiomatous blood vessels having such degenerative changes as fibrosis and thrombosis. The angiomatous blood vessels were found only in the lesion. The ultrastructural features of the neurofibrillary changes were similar to those observed in Alzheimer's disease. Vascular alterations have been suggested to be a possible contributor to the morphogenesis of neurofibrillary changes. In this case the exact etiology of these neuronal changes remains unclear, however, the possibility of a regional vascular role is considered with respect to their morphogenesis.