Features of the duodenal mucosa structure in aging were studied. Investigations were carried out on the basis of aspiration biopsy materials taken from 30 elderly (60-74 years) and 9 senile persons. The duodenal mucosa in persons aged 20-26 years was studied as controls. No gastrointestinal disorders were recorded in the anamnesis of all the persons under study. It is established that with advancing age in the duodenal mucosa atrophy processes start to develop. The number of goblet cells in the crypts and on the villi decreases. The function of Paneth's cells and that of duodenal glands weakens. The epithelium still retains considerable mitotic and amitotic activities, however, possibilities for replacing the rapidly wearing out epithelium of villi in old age are limited.