OBJECTIVE : To identify the differences between ultrasound (US) features of parathyroid carcinoma (PC) and benign parathyroid (BP) lesions in patients with primary hyperparathyroidism (PHPT). METHODS : Twenty-one patients with PC and 64 consecutive patients with BP, whose diagnoses were confirmed at surgery, were enrolled from January 2013 to December 2018. The US features, demographic, clinical, and biochemical characteristics of the two groups were compared retrospectively. RESULTS : There are no significant differences between the patients with PC and BP regarding mean age or mean ionized calcium levels but differences were seen in sex distribution and mean parathyroid hormone (PTH) levels. On US imaging, PC significantly exhibited higher incidences of larger size and higher depth/width (D/W) ratio, heterogeneous echotexture, irregular shape, non-circumscribed margin, intra-nodular calcifications, indistinct border, cystic change, and the presence of suspicious lymph nodes compared to BP lesions. CONCLUSIONS : Preoperative ultrasonography is helpful to differentiate PC and BP. Patients with PC are differentiated from BP by their sex distribution, mean PTH levels, and major US characteristics: larger size, higher D/W ratio, heterogeneous echotexture, irregular shape, non-circumscribed margin, indistinct border, intra-nodular calcifications, cystic change, and the presence of suspicious lymph nodes.