Is severe calcification of a thyroid cyst serious? It depends on the situation. Firstly, a thyroid cyst is not an independent disease; it develops from a simple goiter, nodular goiter, or regressive changes in a thyroid adenoma, some of which may be due to bleeding or necrosis caused by thyroid cancer, forming a thyroid cyst. Therefore, a thyroid cyst could potentially be a malignant indicator. Moreover, the calcification of thyroid cysts mainly depends on the description of the calcification. For instance, some are fine punctate microcalcifications, which are less than or equal to 1mm, while others are larger, coarse calcifications larger than 1mm, and there are even some annular calcifications. Thus, thyroid cyst calcification is not necessarily cancerous, and the likelihood of malignancy varies with each type of calcification, generally, the potential for malignancy is microcalcification greater than coarse calcification, greater than annular calcification. Therefore, whether calcification of a thyroid cyst is serious mainly depends on whether it is a malignant lesion.