Knowledge of the role of interleukin 17 (IL-17) has led to the identification of new subpopulation of T helper lymphocytes – Th17 and T cytotoxic lymphocytes secreting IL-17 (Tc17). An increasing amount of attention is paid to their role in anti-tumor immunity. Aim: The aim of this study was to evaluate the percentage of peripheral blood, peritoneal fluid and cancer tissue CD4+ and CD8+ T lymphocytes producing IL-17 in patients with ovarian cancer. Material and Methods: Forty patients operated due to advanced ovarian carcinoma and twenty-four patients with functional follicle ovarian cysts were recruited. Peripheral blood, peritoneal fluid and cancer tissue mononuclear cells from ovarian cancer patients were stimulated for 4 hours ex vivo with phorbol myristate acetate (PMA) (50ng/ml) and ionomycin(1μg/ml). The percentage of CD4+ and CD8+ T cells producing IL-17 was measured using flow cytometry. Results: CD4+ and CD8+ T lymphocytes producing IL-17 were detected in the peripheral blood, peritoneal fluid and cancer tissue of ovarian cancer patients. The percentage of CD4+ T cells producing IL-17 was higher in the peripheral blood, peritoneal fluid and cancer tissue when compared to CD8+/IL17+ T cells. The percentage of CD4+/IL-17+ was significantly higher in cancer tissue compared to T cells derived form peripheral blood. There was no difference in the percentage of CD4+/IL-17 + T cells between peripheral blood and peritoneal fluid and peritoneal fluid and cancer tissue of ovarian cancer patients. There was no difference in the percentage of CD8+/IL-17+ T lymphocytes in the peripheral blood, peritoneal fluid and cancer tissue in patients suffering from ovarian cancer. Conclusions: Increased percentage of CD4+/IL-17+ and CD8+/IL-17+ T cells in cancer tissue indicates that these cells are accumulated in ovarian cancer microenvironment.