A 55-year-old man showed progressive mental deterioration over a five-year period along with a syndrome of "normal pressure hydrocephalus." At autopsy the main finding was the presence of two age-related neurocellular changes, the neurofibrillary tangle and the Lewy body, in limbic structures and in the pigmented nuclei of the brain stem. Cortical changes were mild, and senile plaques were not present. Electron microscopy occasionally showed an intimate relationship between the paired helical filaments of the neurofibrillary tangle and Lewy bodies in nerve cell processes in the hypothalamus. The findings suggest a closer relationship between Lewy bodies and neurofibrillary tangles than usually suspected. We also speculate that the presence of one type of age change in the brain may accelerate or predispose to other age changes.