Thyroid nodule hypoechoicity is an ultrasound characterization of thyroid nodules. Thyroid nodule hypoechoic means that the nodule echoes are lower than the surrounding thyroid parenchyma. Hypoechoic or very hypoechoic echoes are generally considered to be a characteristic ultrasound feature of suspected malignancy and may be a bad sign. If hypoechoicity is used as a diagnostic criterion, the sensitivity of the diagnosis is high and the specificity is low. Color ultrasound provides a comprehensive assessment of the size, shape, blood flow, and echogenicity of thyroid nodules. In case of abnormalities, a puncture biopsy may be required to clarify the nature of the nodule. Patients with thyroid nodules are advised to consult their doctors at regular hospitals for relevant examinations and treatments.