To describe a case of parathyroid carcinoma localized to ectopic parathyroid tissue within the thymus and the development of hungry bone syndrome postoperatively.We present pertinent clinical, radiologic, pathologic, and laboratory details of the study patient and discuss the relevant literature.A 33-year-old man who presented with only symptoms of fatigue and depression was found to have high serum calcium, parathyroid hormone, and alkaline phosphatase levels. A sestamibi scan revealed evidence of activity adjacent to the sternum. He underwent neck exploration after selective staining of the parathyroid glands with methylene blue dye. A mass was found in the thymic bed, and the pathologic features were consistent with parathyroid carcinoma. Postoperatively, symptoms and signs of hypocalcemia developed despite normal serum calcium levels.Physicians should be aware that (1) parathyroid carcinoma may originate wherever ectopic parathyroid tissue is found and patients may have only nonspecific symptoms, (2) wide local excision is imperative if carcinoma is suspected, and (3) symptoms and signs of hypocalcemia may be evident even when the serum calcium concentration is normal, if it has rapidly declined from a high level.