From 1942 to 1984, 301 operations were performed for hyperparathyroidism; nine patients (3%) had carcinoma. The mean serum calcium level of the patients with carcinoma was 14.0 mg/dl, whereas the mean serum calcium level of patients with benign hyperparathyroidism was 12.0 mg/dl. With follow-up ranging from 2 to 16 years, there has been one death 9 years after the initial operation caused by primary lung cancer. At autopsy the patient also had a recurrence of parathyroid carcinoma in the neck. There were no additional recurrences or deaths. Prognosis was not correlated with any laboratory or pathologic findings. The importance of intraoperative recognition at the time of the initial operation is stressed. En bloc resection is recommended, including ipsilateral thyroid lobectomy and dissection of the tracheoesophageal groove. Radical neck dissection is performed only for extensive cervical node metastases or for reoperations where scarring prevents accurate delineation of the extent of the tumor.