The aim of the present article is to analyze of dietotherapy as employed by Roman physicians in the treatment of therapeutic diseases since one of the important methods of successful treatment and recovery is a properly formulated diet. The subject of this study is De Medicina, the work of Aulus Cornelius Celsus, the renowned Roman scholar and encyclopedist, the author of an eight-volume medical treatise, which summarizes the experience of ancient medicine in the fields of therapy, surgery, pathology, and dietetics. To achieve the stated objective, a comprehensive application of general scientific and specialized research methods was employed, including analysis, synthesis, induction, deduction, historical, interdisciplinary, descriptive methods, and contextual analysis. This approach allowed for the clarification of the peculiarities of nutrition in the prevention and treatment of internal organ diseases. Critically summarizing the achievements of medicine in therapy, surgery, and pathology, Celsus consistently emphasized the importance of diet therapy in the treatment and prevention of diseases. It has been established that even in ancient times, the nutrition of a sick person was considered the fundamental basis upon which other therapeutic measures should be applied. Dietary nutrition was aimed at reducing the risk of complications, restoring the body, and preventing diseases. The main principles of ancient diet therapy were based on the following: aligning the diet with the physiological needs of the body during illness, adapting food processing methods for specific diseases, determining the duration of the diet depending on the characteristics of the disease's progression.