Objective: Numerous studies suggest that cyclooxygenase-2 (COX-2) is overexpressed in cancer. Our objective was to investigate the relationship between COX-2 expression in ovarian carcinoma and clinicopathological factors. An emphasis was put on the association with the new pattern of tumorigenesis that divides tumors into type I – less aggressive, and type II – more aggressive one. The prognostic significance of COX-2 expression was evaluated. Methods: Ovarian cancer tissues were obtained from 65 patients in FIGO III stage (23 with type I and 42 with type II ovarian cancer). COX-2 expression was evaluated by immunohistochemistry. The statistical analysis was performed in order to assess the connection between COX-2 expression and characteristic factors of ovarian cancer patients as well as the new division for type I and type II ovarian cancer. Results: COX-2 expression was detected in 91% of tissue samples. It was markedly elevated in well differentiated tumors (p=0.0041). The platinum - resistant tumors had significantly higher expression of COX-2 (p=0.0337). There was no difference between COX-2 expression in type I and type II ovarian cancer (p=0.6720). The COX-2 staining was not associated to age, CA125 level, the presence of ascites or any special histological type. An increased expression of COX-2 was an unfavorable prognostic factor for overall survival (p=0.0369) and progression-free survival (p=0.0218). Multivariate analysis confirmed that COX-2 overexpression is an independent unfavorable prognostic factor of shorter progression-free survival (p=0.048). Conclusions: COX-2 expression is an unfavorable prognostic factor for progression-free survival and overall survival in ovarian cancer. There is no relationship between COX-2 expression in ovarian cancer tissue and the examined model of ovarian cancer pathogenesis.