Background:The clinical behavior and management of poorly differentiated thyroid carcinoma (PDTC) are very different from papillary thyroid carcinoma (PTC).By comparing the clinical and ultrasonographic features between the two tumors,we proposed to provide more possibilities for recognizing PDTC before treatment.Methods:The data of 13 PDTCs and 39 age-and gender-matched PTCs in Peking Union Medical College Hospital between December 2003 and September 2013 were retrospectively reviewed.The clinical and ultrasonic features between the two groups were compared.Results:The frequencies of family history of carcinoma,complication with other thyroid lesions,lymph node metastases,recurrent laryngeal nerve injuries,and distant metastases were higher in PDTCs (30.8％,61.6％,69.2％,23.1％,and 46.2％,respectively) than those in PTCs (2.6％,23.1％,25.6％,2.6％,and 2.6％,respectively) (P ＜ 0.05).The mortality rate of PDTCs was greatly higher than PTCs (P ＜ 0.01).Conventional ultrasound showed that the size of PDTCs was larger than that of PTCs (3.l ± 1.9 cm vs.1.7 ± 1.0 cm).Clear margins and rich and/or irregular blood flow were found in 92.3％ of PDTCs,which differed substantially from PTCs (51.7％ and 53.8％,respectively) (P ＜ 0.05).Conclusions:PDTC is more aggressive and its mortality rate is higher than PTCs.Accordingly,more attention should be given to suspicious thyroid cancer nodules that show large size,regular shape,and rich blood flow signals on ultrasound to exclude the possibility of PDTCs.