Calcification refers to calcium deposits within the nodule due to a variety of causes, and when the reflected interface acoustic impedance is large, it is manifested on ultrasound images as strong echogenicity in various forms with or without acoustic shadowing posteriorly. According to the size, morphology and distribution characteristics of calcifications, they can be classified as microcalcifications, coarse calcifications, marginal calcifications and calcified spots. Among them, microcalcifications are mostly calcifications and fibrillations secondary to amyloid deposits within the sarcoid or medullary carcinoma, while coarse calcifications, marginal calcifications and calcified spots are usually caused by malnutrition. Microcalcifications appear as punctate strong echogenicity with or without posterior acoustic shadowing and are seen in 40% to 61% of papillary carcinomas, but also in other benign and malignant lesions, such as follicular carcinoma, poorly differentiated carcinoma, nodular goiter, follicular adenoma and Hashimoto’s thyroiditis. Coarse calcifications are most often seen in benign nodules, especially nodular goiters. Marginal calcifications refer to calcifications located at the marginal areas of thyroid nodules and are commonly seen in nodular goiters, which are a sign of benign nodules. There are 3 types of marginal calcifications: type 1, speckled, with microscopic or coarse nonlinear particles; type 2, curved, with smooth margins; and type 3, curved, with irregular margins. Calcifications can also be classified as arcuate or circumferential depending on whether they are confined to part of the lesion or involve the entire lesion. Calcified spots are single coarse foci of calcification and do not show thyroid nodules on ultrasound in the area of calcification and are commonly seen in benign thyroid lesions, such as nodular goiter, hyperthyroidism, and other diffuse thyroid disorders.