The purpose of the present study was to evaluate preoperative CA125 as a prognostic factor in stage I epithelial ovarian cancer (EOC). Preoperative serum CA125 levels from 118 women with FIGO (International Federation of Gynaecology and Obstetrics) stage I EOC were analysed and the prognostic value was evaluated and compared with other prognostic factors (age, grade, substages, histologic type). By the Kaplan-Meier estimate we demonstrated that patients with stage I EOC and preoperative serum CA125 levels <65 U/mL had a significantly longer survival compared to stage I EOC patients with preoperative serum CA125≥65 U/mL (p=0.01). The results from the present study may be useful for decision making respecting postoperative chemotherapy in stage I EOC patients. Serum CA125 levels might therefore be included as a prognostic factor in future clinical trials of stage I EOC.