A MALIGNANT tumor arising in the parathyroid glands presents an appropriate topic for discussion because there has not yet been a common understanding among writers of what constitutes carcinoma of these glands. Usage in many instances of the piquing term malignant adenoma attests to this fact. From the data given in many reports of cases in the literature, it is evident that the diagnoses were in error. The early reports of carcinoma showing no evidence of hyperparathyroidism are especially inconclusive. Carcinoma of the thyroid gland has been mistaken most often for a malignant tumor of the parathyroid glands. In more recent years, since there has been some understanding of the physiology and a better knowledge of the anatomic variations and cytology of these glands, it has been possible to come to a more definite opinion of the nature of the tumor. Analysis of the reports since 1902 of parathyroid tumors