The effeciency of combined application of isotope scan and ultrasonography of thyroid was assessed in 91 patients with thyroid nodule. Malignancy rates were 35.5%, 18.8%, & 0% in solid, complex & cystic nodule group, respectively. No statistically significant co-relationship was found between isotope scan finding & ultrasonographic finding. Malignant nodules were found only in cold solid nodule group & cold complex nodule group, and rate of malignant nodule was different between them(45.8% in cold solid nodule group & 20.7% in cold complex nodule group). Difference between the rate of cystic change in benign & malignant nodule observed in our study(59.2% vs. 35.3%) was thought to explain at least partly the statistically different rate of malignant nodule in cold solid nodule & cold complex nodule group. No difference in the boundary condition, echogenicity & distribution of internal echo existed between benign nodule group &malignant nodule group.