The hypothalamic lateral tuberal nucleus (NTL) was studied in the formalin- fixed brains of five patients with Huntington's disease (HD) and in five ageand sex-matched controls. With the Kluver-Barrera (luxol fast blue/cresyl violet) and hematoxylin and eosin stains the NTL was denned by its cytoarchitectonic characteristics. The nucleus was composed of one type of neuron and had about 60,000 cells. In HD, up to 90% neuronal loss was found in the NTL. The remaining neurons showed features of degeneration and there was astrocytosis. The estimated total number of glial cells in the NTL was reduced to 80% of the control values, which was exclusively accounted for by a reduction of 40% in the number of oligodendrocytes. The total number of astrocytes was unchanged. Grouping of astrocytes and the changes observed in glial fibrillary acidic protein immunocytochemistry suggested that astrocytic proliferation occurred.