Abstract: Objective: To investigate the calcification of thyroid nodules detected by ultrasound and its relation with thyroid carcinoma. Methods: One hundred and seven cases of calcified thyroid nodules seen in our hospital during a period of one year were examined by high-resolution colored ultrasonography preoperatively. The percentage of malignancy found in those calcified nodules in different sexes, ages and calcification groups was retrospectively reviewed. Results: Fifty-six cases of calcified nodules were confirmed postoperatively to be thyroid papillary carcinoma by pathology (52.3%). There was a significant difference in the percentages of malignant calcified nodules between the different age groups (38.6% for patients of 45 and older, 68% for patients younger than 45; P=0.002). There was no significant difference in the percentage of malignant calcified nodules between the male and female groups (72.7% and 50%, respectively; P=0.153). However, there was a significant difference in the percentage of malignant calcified nodules between the group with microcalcification and the group with coarse calcification (78.8% and 40.5%, respectively; P<0.001). Conclusion: Detection of calcification inside thyroid nodules has a clinical significance in the diagnosis of thyroid carcinoma. Microcalcification is a highly specific sign that predicts thyroid malignancy, especially papillary carcinoma.