The incidence of parathyroid carcinoma in patients surgically treated for primary hyperparathyroidism at the University of Michigan Hospital was 0.4% during an 18-year period. The courses of the five patients with metastatic disease are described. Histologic reevaluation and assessment of the DNA ploidy pattern were performed in each case. Localization studies preceded all reexplorations. The number of operative procedures in each patient ranged from two to 10. Two patients are living with recurrent disease and one has been disease free for 42 months. Two patients died after 2 and 12 years, respectively. Three patients had aneuploid tumors; one had a diploid tumor. One patient had both aneuploid and diploid cell populations. Dilemmas in diagnosis, localization, and medical and surgical management were encountered in patients with metastatic carcinoma. The chosen treatment should be evaluated individually in each case because of the variability in aggressiveness of this malignancy. Surgical resection proved most effective in some of these patients for both local and distant recurrences. Bisphosphonates and gallium nitrate have been reported to be effective in controlling hypercalcemia. Only the former had some effect in one of our patients.