PURPOSE: We aimed to find out the morphological differences between malignant and benign thyroid nodules by ultrasonographic findings. MATERIALS & METHODS: We included 46 benign nodules and 23 malignant ones which were all confirmed pathologically by surgery or cytology. Ultrasonography was performed to analyze the presence of lobulation, the presence and thickness of halo, echogenicity and heterogeneity of internal echo, internal calcification and cystic change, size of nodule, and cervical lymphadenopathy. For statistical analysis, chi-square test was used. RESULTS: Lobulation was seen in 16(69.5%) of malignant and 5(10.8%) of benign nodules(p < 0.01). Thick and irregular halo was ween in 11/17 cases(64.7%) of malignant and 4/37 cases(10.8%) of benign nodules(p < 0.01). Low echogenicity was seen in 18(78.3%) of malignant and 4(8.7%) of benign nodules(p < 0.01). Heterogeneous internal echo was seen in 12(52.2%) of malignant and 8(17.4%) of benign nodules(p < 0.05). Calcification was seen in 11(47.8%) of malignant and 3(6.5%) of benign nodules(p < 0.01). Nodules without cystic change were seen in 17 (73.9%) of malignant and 21(45.7%) of benign nodules(p < 0.05). The presence of halo and the size of nodules did not corrlate statistically in determining malignant or benign nodules(p > 0.05). None of cervical lymphadenopathy was present in cases of both malignant and benign nodules. CONCLUSION: Lobulation, thick and irrehular halo, low and heterogeneous internal echo, calcification, absenice of cystic change are the findings that suggest malignancy in thyroid ultrasonography.