Hypothesis/aims of study. Endometriosis is a disease characterized by proliferation of tissue that is similar in morphology and function to the endometrium, outside the uterine cavity. Thanks to the theory of J. Sampson (1927), which explains endometrioid heterotopia formation by bits of endometrial tissue migrating through the fallopian tubes during menstruation and their subsequent implantation in the pelvis, research has begun on the biological properties of eutopic endometrial cells in women with endometriosis, which is still relevant today. The present study was aimed to assess the activity of nucleolus organizers in the endometrium in women with external genital endometriosis and without it at different stages of the menstrual cycle. Study design, materials, and methods. Paraffin blocks of endometrial biopsy specimens were taken from 68 women with and without external genital endometriosis. The activity of nucleolar organizers was evaluated by the method of J. Crocker (1983). Results. The data obtained showed a significant increase in ribosomal activity in the cells of the endometrial glandular and surface epithelium in women with external genital endometriosis at the stages of late proliferation, as well as early and middle secretions. There was also a significant decrease in the activity of the nucleolar organizers of endometrial epithelial cells at the stage of late secretion in women with external genital endometriosis. Conclusion. The obtained differences in regulation of ribosomal synthesis in the cells of the integument and glandular epithelium of the endometrium in women with external genital endometriosis, in our opinion, can provide an increase in the total amount of epitheliocytes of the endometrium, increase their adhesive and invasive abilities, and lengthen the life cycle of cells. This contributes to the formation of endometrioid heterotopies and the development of external genital endometriosis. Changes in the activity of nucleolar organizers in the endometrium in women with external genital endometriosis may be of clinical interest for the diagnosis of this pathology.