Purpose: The aim of this study was to determine the frequency of endometriosis in epithelial ovarian cancer patients. Methods: Patients who had undergone epihelial ovarian cancer surgery between 2000 and 2004 were subjected to a retrospective analysis. The analysis focused on the presence of ovarian endometriosis, histological types and stages of ovarian cancer, treatment types and five-year survival rate. Results: Out of the 210 operated ovarian cancer patients, 23 had coexisting ovarian endometriosis. Ovarian endometriosis was detected in 3.5% (4 of 113 patients) of cases with serous ovarian cancer, in 31.69% (12 of 38 patients) of cases with endometrioid, and in 36.8%e (7 of 19 patients) of cases with clear cell ovarian cancer. The treatment of ovarian cancer patients was acombination of surgery and chemotherapy. Conclusion: Endometriosis was most frequently present in patients with clear cell (36.8%)and endometrioid ovarian cancers (31.6%). The five-year survival rate for ovarian cancer patients in all stages was 39.1%.