Aim of paper: The aim of paper was to assess the prognostic value of preoperative CA 125 level in patients with late-stage ovarian cancer, particularly in correlation with optimal cytoreduction rate and duration of symptom-free survival. Material and methods: Retrospective analysis included 76 patients with FIGO stage III ovarian cancer. Using the uni- and multivariate models, prognostic value of the following parameters was assessed: preoperative CA 125 level, clinical stage, histological type and grade of maturity in correlation with quality of cytoreduction and symptom-free survival. Results: Baseline CA 125 serum level in the entire study population ranged from 35 to 9740 IU (median: 1117 IU). Optimal cytoreduction rate for the entire population was: 73.7% for CA 125 level below 288 IU, 47.4% for CA 125 level 288-1118 IU, 26.3% for CA 125 level 1119-2880 IU and 15.8% for CA 125 above 2880 IU (p=0.019; χ2). In the logistic-regression model, only CA 125 level had a significant influence on quality of cytoreduction. Analysis of correlation of other prognostic factors on symptom-free survival revealed, that only CA 125 and histological maturity grade correlated significantly with survival. Conclusions: Preoperative serum CA 125 level is significantly correlated with optimal cytoreduction rate achieved, as well as with risk of death and symptom-free survival.