Affiliation. Federal state budgetary educational institution of higher education «North-Western State Medical University named after I. I. Mechnikov» under the Ministry of Health of the Russian Federation, Saint-Petersburg Introduction. Elevated level of transforming growth factor-61 (TGF-61) can be the cause of impaired immune response among women with endometriosis due to its ability to reduce the activity of NK-cells, which contributes to the survival of ectopic endometrial cells in the abdominal cavity and plays a key role in the progression of the disease. Materials and methods. 196 endometrioma observations were studied, an immunological study of peripheral blood was performed with the determination of CD3-CD16/56+ (natural killers) and an IHC study of the expression of TGF-61 in the capsule of an endometrioid cyst and in a preserved cytogenic stroma. The IHC study showed that the expression area of TGF-61 was significantly larger in the surgical material in the recurrent course of endometriosis; an immunological study revealed a significant decrease in NKcells during the endo-metrioma recurrence. Conclusion: Further study of the relationship between TGF-61 and NK cells may be important as prognostic markers of recurrent endometriosis.