Background. No consensus exists which patients with surgical stage I epithelial ovarian should receive postoperative chemotherapy. The purpose of this study was to evaluate the prognostic impact of preoperative CA-125 and to establish a prognostic index to identify patients in different risk categories. Methods. Data of 600 surgically staged patients with FIGO stage 1 EOC treated in eleven gynecological cancer centers in Australia, the USA and Europe were analyzed. Eligible patients include those with invasive EOC where a preoperative CA-125 was obtained and standard surgical staging performed. Overall survival (OS) was chosen as study endpoint. Preoperative CA-125 values were compared with other prognostic factors, and univariate and multivariate Cox models were calculated. Results. Two hundred and one patients (33.5%) had preoperative CA-125 30 U/ml, respectively (p 0.003). Multivariate analysis confirmed preoperative serum CA-125 > 30 U/ml (OR 2.7) and age at diagnosis > 70 years (OR 2.6) as the only independent predictors for overall survival. Conclusion. Pretreatment of CA-125