The objective is to assess the ability of preoperative serum CA125 levels to identify patients at high risk of suboptimal cytoreductive surgery for epithelial ovarian cancer (EOC). One hundred and thirty-two women diagnosed with EOC between 1998 and 2004, who had serum CA125 levels measured preoperatively and received primary cytoreductive surgery, were retrospectively evaluated. The value of CA125 and patient and disease characteristics to predict suboptimal cytoreduction were determined, and a prognostic scoring system, based on statistically significant variables, was created. Optimal cytoreduction was achieved in 42.7% of the women with FIGO stage III/IV EOC. The optimal cutoff point of preoperative CA125 to predict surgical outcome in this group was 330 U/mL (sensitivity 80.0%; specificity 41.5%). The area under the receiver-operating characteristic curve (AUC) for preoperative CA125 predicting suboptimal surgery in FIGO stage III/IV was 0.576 (P = 0.617). Preoperative radiologic amount of ascites and weight loss (ie, >or=10% in the last 6 months before diagnosis) were independent prognostic factors for suboptimal cytoreduction, showing an AUC of 0.76 (P < 0.001) in women with FIGO stage III/IV. A prognostic scoring system showed that the chance of suboptimal surgery was 84.6% in FIGO stage III/IV when both these factors are present preoperatively. The role of CA125 levels predicting suboptimal cytoreduction seems questionable. Instead, women with considerable weight loss and a gross amount of ascites have a higher risk of suboptimal cytoreduction. These patients may be candidates for neoadjuvant chemotherapy.