We analyzed 40 cases of high resolution US findings of thyroid carcinoma proven by surgical or needle biopsy. The results were as follows: 1. The incidence was predominent in female(M/F=1:5.6). 2. Recent increase of the tumor size or the size over 5cm accompanying mass effect upon adjacent structures(such as trachea) was proved as significant findings of malignancy. 3. The nature of the masses showed solid in 30 cases (75%) complex in 10 cases (25%) of which 5 cases(12.5%) were prodominently cystic. 4. The echo pattern of the masses was hypoechoic in 21 cases (70%) hyperechoic in 6 cases (20%) and isoechoic in 3 cases (10%) Heteropeneous in 23 cases(10%) Hemogeneus in 7 cases (18%) 5. Internal calcification of the masses were observed in 13 cases (32.5%) The nature of calcifications was small multiple irregular punctate in all cases. 6. Halo sign were present in 20 cases(50%) 7. Invasion of adjacent structures: Lymph node in 10 cases(25%) Muscles in 5 cases(12.5%) Trachea in 2 cases(5%) 8. The accuracy of preoperative sonographic diagnoisis was 62.5%s