The preoperative Ca-125 levels of 426 patients with Stage III/IV ovarian carcinoma from a single institution were correlated with surgical outcome. Optimal was considered the cytoreduction if the largest residual tumor was<or equal to 1 cm in diameter. Receiver operation characteristic (ROC) curve data were combined with interval likelihood ratios at various Ca-125 levels to determine the cut-off level with the maximum prognostic power