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 adenomatoushyperplasia, 21 of papillary adenocarcinoma, and 7 of follicular adenocarcinoma) were analyzed. Colour signalanalysis was performed by inspecting the signals in and around the nodules, and these were graded from 0 to IIIaccording to the degree of vascularity in internal and marginal blood flow. Peak systoic velocity (PSV) andresistive 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, withstatistical significance(P<0.05). In spectral wave analysis, correlation between PSV and malignancy of thyroidnodules 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 thedifferentiation of benign and malignant lesions of thyroid nodules.