To assess their usefulness in the prediction of tumor recurrence, we retrospectively examined the accuracy of preoperative diagnosis of ovarian cancer based on tumor markers on 279 patients with benign and malignant ovarian tumors treated at our department. Of the tumor markers examined, CA125 had the highest diagnostic accuracy, suggesting that it is the most useful marker in the diagnosis of ovarian cancer. TPA and IAP were found to be relatively useful, the tumor markers recently identified, CA72-4 had a high true positive rate. We examined the factors affecting the cut-off value for CA125 in healthy volunteers and determined the corrected cut-off value. Using this value, we assessed the usefulness of CA125 in distinguishing between benign and malignant tumors and in predicting tumor recurrence. Factors found to affect the serum CA125 level included pregnancy, menstrual cycle, dysmenorrhea, menopause, and blood type. Using our equation for women over 40 years of age, we obtained a specific cut-off level of 16 U/ml for postmenopausal women, which was found to more accurately distinguish between ovarian tumors in this age group than did the conventional cut-off level of 35 U/ml, which has been used for all age groups. Furthermore, the specific cut-off level predicted tumor recurrence about 2 months earlier than did the conventional cut-off value. In tumor recurrence, CA125 had risen gradually but was within the normal range. Tumor recurrence was observed in all patients who had shown continuous three-stage elevation of CA125 within the normal range.