The numbers of neurons in nine different hypothalamic nuclei were counted in every eighth section of serially-cut hypothalami in young (4 to 6 months) and reproductively senescent (15 to 18 months) female hamsters. There were no morphological differences discernible at the light microscopic level in the hypothalami of the aged hamster. There did not appear to be any significant differences in the lateral or rostral-caudal extent of these nuclei nor in neuron counts in old versus young animals. These results are discussed in light of species differences and possible functional alterations.