PURPOSE: To assess the utility of color Doppler sonography in the differential diagnosis of thyroid nodules. MATERIALS AND METHODS: Fifty patients with thyroid nodules(10 cases of follicular adenoma, 12 of adenomatous hyperplasia, 21 of papillary adenocarcinoma, and 7 of follicular adenocarcinoma) were analyzed. Colour signal analysis was performed by inspecting the signals in and around the nodules, and these were graded from 0 to III according to the degree of vascularity in internal and marginal blood flow. Peak systoic velocity (PSV) and resistive index (RI) in internal vascularity were used to analyse the flow signal. RESULTS: Internal colorsignals of malignant lesions tended to be high grade, whereas those of benign lesions tended to be low grade, with statistical significance(P<0.05). In spectral wave analysis, correlation between PSV and malignancy of thyroid nodules was statistically significant(P<0.05). The value of RI did not correlate with the malignancy of nodules, but tended to show a meaningful difference. CONCLUSIONS: Although further studies may be required, color Dopplersonography using color signal analysis and flow signals analysis is a useful imaging modality for the differentiation of benign and malignant lesions of thyroid nodules.