Purpose : To evaluate the usefulness of color Doppler ultrasonography in the differential diagnosis of breastmasses. Materials and Methods : We prospectively evaluated to pathologically proven breast lesions. Forty-threewere benign (39 fibroadenomas, two papillomas and two lipoma) and 27 were malignant (25 infiltrating ductalcardinomas, one mucinous carinoma and one atypical medullary caricinoma). In 32 cases, we categorized color signalfrom 0 to III, according to the degree of vascularity, and analysed peak systolic velocity (PSV) and resistiveindex (RI). Results : Color signals of malignant lesions tended to be high grade (II, III), whereas those ofbenign lesions tended to be low (0, I), and the difference was statistically significant (P<0.005). In theanalysis of spectral waveform , correlation between RI, PSV and malignancy was statistically significant (P<0.02).RI above 0.7 and PSV above 10 were the highest recorded values for sensitivity and specificity. Conclusion : ColorDoppler ultrasound is a useful modality to distinguish benign from malignant breast masses. Malignancy issuggested when the color signal is grade II or III, the resistive index is higher than 0.7, and peak systolicvelocity is higher than 10cm/sec.