Ultrasonography plays an important role in the diagnosis of thyroid nodules. Certain ultrasound signs can help to differentiate benign from malignant thyroid nodules. Almost all thyroid nodules with the following two types of ultrasound changes are benign: 1) purely cystic nodules; 2) nodules with multiple small vesicles occupying more than 50% of the nodule volume and showing spongy changes, 99.7% of which are benign. The following ultrasound signs suggest the possibility of thyroid cancer: 1) solid hypoechoic nodules; 2) nodules with rich blood supply (under normal TSH); 3) nodules with irregular shape and margin, halo absence; 4) microcalcifications, pinpoint diffuse distribution or clusters of calcifications; 5) abnormal ultrasound images of cervical lymph nodes, such as rounded lymph nodes, irregular or blurred borders, uneven internal echogenicity, internal calcifications, and uneven internal echogenicity. The lymph nodes are round, with irregular or blurred borders, uneven internal echogenicity, internal calcification, indistinct corticomedullary demarcation, loss of lymphatic portals or cystic changes. Note: The ability to identify benign and malignant thyroid nodules by ultrasonography is related to the clinical experience of the ultrasonographer.