Parathyroid carcinoma, although rare, represents 0.5-4.0 per cent of the cases of hyperparathyroidism. The authors have encountered five cases of parathyroid carcinoma in their experience treating 445 patients with primary hyperparathyroidism (1.1%) since 1965. All five patients were women, ranging in age fro 29 to 60 years, and had marked hypercalcemia at the time of presentation, with values up to 26 mg/dl in one case. All the tumors were locally adherent to surrounding structures at the time of parathyroidectomy. Pathologically they were characteristic with a dense sclerotic reaction and fibrous bands criss-crossing islands of parathyroid cells. Three patients with local as well as distant metastases have died as a result of recurrent parathyroid carcinoma (follow-up: 2, 3, and 6 years). The remaining two patients became normocalcemic following resection, and have been asymptomatic for 1 and 7 years, respectively. The overall survival and clinical course, in our limited experience with five parathyroid carcinoma cases demonstrates that the morbidity and mortality in these patients is mainly due to local recurrence with the resultant metabolic disturbances, as has been previously noted in the literature.