To describe a patient with a mediastinal parathyroid carcinoma and hypercalcemia as well as to compare the features of parathyroid carcinoma with those of hypercalcemia due to other causes of primary hyperparathyroidism.We present a case report and discuss the diagnosis and management of this rare tumor.In a 44-year-old man, severe hypercalcemia and normal findings on neck exploration led to referral and ultimate detection of an anterior mediastinal mass. Surgical resection and pathologic examination of the mass revealed a cystic parathyroid carcinoma. Subsequently, normalization of serum calcium and parathyroid hormone levels ensued.Parathyroid carcinoma as an alternative to the diagnosis of primary hyperparathyroidism should be considered in patients with dramatically increased serum calcium and parathyroid hormone levels at the time of initial examination. The mainstay of therapy for parathyroid carcinoma is complete surgical resection. Accurate preoperative localization of parathyroid carcinoma is helpful, especially in instances of reoperation or hypercalcemic crisis.