We studied the best parameter to differentiate preoperatively between malignant ovarian tumors and benign ovarian tumors. From January 1988 to December 1992, 244 patients of ovarian tumor were treated with surgery at Chonnarn University Hospital. Patients diagnosed as malignancy by histopathology were 26.2%(64 patients), As the diagnostic pararnetar, we used age, ultrasonography, tumor markers, CT or MRI. The results were obtained as follows: 1. The predictive value of ultrasonographic examination for ovarian cancer was 73.1%. 2. The predictive value of seren CA-125 level for ovarian cancer was 69.1%. 3. The predictive value of combination af ultrasonographic examination and serum CA 125 level for ovarian cancer was 90%. 4. The predictive value of combination of the age older than 40 years, ultrasonographic examination and serum CA-125 level for warian canrer was 92.3%. 5. The predictive value of comhination of three tumor markers(CA-125, CEA and CA 72-4), ultrasonographic examination, CT and MRI for ovarian cancer was 94.6%. Finally, we could preaperatively most exactly differentiate between malignant ovarian tumors and benign ovarian tumors by use of age, three tumor markers(CA-125, CEA and CA 72-4) and ultrsonography, CT or MRI.