Lewy bodies have been found in the hypothalamic lateral tuberal nucleus (NTL) and the adjoining tuberomammillary nucleus (TM) in Parkinson's disease (PD). The NTL is severely atrophic in Huntington's disease; the TM seems unaffected. In this study, we examined we examined the NTL and the TM of seven PD patients and one patient with presumed PD to assess whether the presence of Lewy bodies indicated neuronal loss. Most Lewy bodies were found in the TM, but they were also present in the NTL of seven of the eight patients. The number of NTL neurons in the PD patients was similar to a group of 14 nonneurological controls, seven Alzheimer's disease (AD) patients, and two AIDS patients with dementia. This challenges the hypothesis that Lewy bodies are a sign of significant cell death. The TM, whose cells could not be counted, did not seem depleted in neuronal numbers, although occasional neuronophagia was observed.