In clinical practice, nodules are generally small masses and occupying lesions found during ultrasound examination of superficial organs. Hypoechoic refers to a nodule or mass with lower internal echogenicity than normal tissue and is a descriptive term for an ultrasound sonogram. Hypoechoic nodules of the thyroid and breast are more common in clinical practice. The echogenicity of nodules varies depending on the composition of the nodule, which can be cystic, solid, or mixed cystic and solid. Cystic nodules are mostly non-echoic, cystic-solid mixed nodules are mostly mixed echogenic, and solid nodules can be hypoechoic, hyperechoic, and strongly echogenic in various ways. The so-called hypoechoic nodule is an ultrasound description of the nodule, and the function and nature of the nodule cannot be judged simply by the fact that the nodule’s echo is hypoechoic. A hypoechoic nodule is usually a solid nodule. If one wants to have a further understanding of the nodule, then the sonographer needs to observe more information, such as the nodule morphology, boundary and internal echoes as well as the blood flow of the nodule to make a comprehensive judgment. For example, whether the nodule is regular in shape, whether the border is clear and smooth, whether there is an intact envelope, whether the internal echogenicity is uniform, and whether the blood flow inside and around the nodule and the resistance index of the blood flow are all necessary to make a comprehensive diagnosis and to grade the nodule by ultrasound. In general, nodules with grade 2 and 3 are recommended for regular observation, while nodules with grade 4 or higher are recommended for further examination or surgery in most cases due to the possibility of malignancy.