PURPOSE: To evaluate the usefulness of color Doppler ultrasonography in the differential diagnosis of breast masses. MATERIALS AND METHODS: We prospectively evaluated to pathologically proven breast lesions. Forty-three were benign (39 fibroadenomas, two papillomas and two lipoma) and 27 were malignant (25 infiltrating ductal cardinomas, one mucinous carinoma and one atypical medullary caricinoma). In 32 cases, we categorized color signal from 0 to III, according to the degree of vascularity, and analysed peak systolic velocity (PSV) and resistive index (RI). RESULTS: Color signals of malignant lesions tended to be high grade (II, III), whereas those of benign lesions tended to be low (0, I), and the difference was statistically significant (P<0.005). In the analysis 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: Color Doppler ultrasound is a useful modality to distinguish benign from malignant breast masses. Malignancy is suggested when the color signal is grade II or III, the resistive index is higher than 0.7, and peak systolic velocity is higher than 10cm/sec.