Parathyroid adenomas are subdivided into chief cell and oxyphil cell variants. However, the parathyroid carcinomas described thus far have been only of the chief cell type. Two cases of oxyphil cell carcinoma of the parathyroid gland are reported, with light and electron microscopic study. The patients presented apparent clinical hyperparathyroidism with x-ray finding of generalized fibrous osteitis and palpable parathyroid tumors. Initially, a pathologic diagnosis of parathyroid adenoma was made in both of them. However, in due course, pulmonary metastases developed in one patient and a local recurrence occurred in the other, 5 and 8 years after the primary operation, respectively. Review of the microscopic slides showed that both primary tumors met the criteria of parathyroid carcinoma. A matter of interest in both cases is that the neoplasms were composed principally of oxyphil cells. Electron microscopic study confirmed the existence of typical oxyphil cells packed with numerous mitochondria.