The hypothalamic lateral tuberal nucleus was investigated in 5 young patients, aged 45 to 64 years, with Alzheimer's disease (AD) and in 5 age-matched control subjects. Combining conventional histopathological and immunocytochemical staining with neuronal counts, a peculiar form of neuronal pathology was characterized. Although neurons and neurites in the lateral tuberal nucleus of AD specimens were heavily stained by Alz-50, silver and thioflavine-S stains disclosed few neurofibrillary tangles or neurites. The numbers of neurons in the lateral tuberal nucleus of patients with AD (67,450; SEM = 5,050) were no different from those of control subjects (58,900; SEM = 2,450). In the AD patients, few plaques were present and were almost exclusively of the amorphous variety. We conclude that neurons in the lateral tuberal nucleus show an early stage of AD-related cytoskeletal pathology (Alz-50 positivity), but without plaques or neuronal death.