When parathyroid carcinoma occurs in the thyroid gland, it is very difficult to diagnose before surgery because imaging studies and aspiration cytology cannot distinguish parathyroid carcinoma from thyroid nodule or benign parathyroid disease. A 53-year-old male was referred to our hospital for assessment of hypercalcemia. He had suffered from chronic kidney disease for 13 years. A 2.5×1.5 cm hypoechoic nodule was noted in the left thyroid gland on ultrasonography, and it showed increased

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... on the sestamibi scan. Fine needle aspiration biopsy revealed it to be a parathyroid lesion, which was confirmed by surgery as parathyroid carcinoma completely surrounded by normal thyroid parenchyme. Because ultrasonography and aspiration cytology have only a limited role in distinguishing parathyroid carcinoma from thyroid neoplasm, suspicion of parathyroid carcinoma before or during surgery through careful examination can lead to complete resection at the initial surgery. This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (https://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.