Since early detection of ovarian cancer is difficult, most cases are diagnosed at advanced stages. The imaging diagnosis is based on pattern classification and is limited with respect to the precise determination of malignancy. High-frequency transvaginal sonography improves the ability to detect malignant ovarian tumors over that of transabdominal route, however, the predictive values are unsatisfactory because of inability to distinguish between malignant and benign tumors that have similar morphologic characteristics. The introduction of transvaginal colour flow imaging has allowed detection of low-resistance intratumoral blood vessels, characteristic of malignant tumors, and visually reflected the state of blood flow of an ovarian tumor. These two ultrasonographic methods were used for diagnosis of ovarian tumors in 65 women treated in our Department of Obstetrics and Gynecology. Waveforms of the parenchymal tumor arteries or tumor surface arteries were compared using value of the resistance index (RI). The sensitivity, specificity and accuracy of the preoperative RI in detecting malignant ovarian tumors were 100%, 94%, 95.4% respectively. The sensitivity, specificity and accuracy of preoperative suspicious sonographic findings in detecting malignant ovarian tumors were 100%, 61% and 71%. Positive and negative predictive values of colour flow imaging were 85% and 100%, whereas for grey-scale transvaginal ultrasonography they were 46% and 100% respectively. The findings of this study suggest that transvaginal colour Doppler is a method which is superior to the other methods for preoperative evaluation of ovarian malignancy.