OBJECTIVES: Endometriosis is a complex, chronic inflammatory disease in which immune system disorders play an important role. Soluble mediators of the immune and inflammatory response, including cytokines, are involved in these processes. Therefore, the aim of the conducted research was to understand the role of selected cytokines belonging to the Interleukin-1(IL-1) family, including IL-36α, IL-36β, IL-36γ, IL-36R, IL-37 and IL-38, in the onset and development of endometriosis by analysing the concentration of the tested molecules and to determine whether their concentration depends on the stage of the disease. MATERIAL AND METHODS: The study group included 60 women who had pelvic endometriosis diagnosed during laparoscopy and subsequently confirmed by histopathology. The reference group consisted of 20 women who had no endometriosis or other pelvic lesions during laparoscopy. RESULTS: Immunoenzymatic assays were used to determine the concentration of the cytokines studied. In the peritoneal fluid of women with endometriosis, a statistically significant increase in the concentrations of all parameters tested was observed: IL-36α, IL-36β, IL-36γ, IL-36R, IL-37 and IL-38. The concentration of these cytokines depended on the severity of the disease. CONCLUSIONS: Disturbances of the immune system involving the network of cytokines belonging to the IL-1 family occurring in the peritoneal fluid environment testify to the involvement of these molecules in the development of the disease and are one of many factors involved in the pathogenesis of endometriosis. The use of some of them in the treatment of endometriosis may be a hope for effective causal treatment of this disease, but this requires further, more advanced research.