No clinical or laboratory data allow a preoperative diagnosis of parathyroid carcinoma and only occasionally does a definitive finding differentiate an adenoma from a carcinoma. We present a case of primary hyperparathyroidism presenting with severe elevation of parathyroid hormone and serum calcium as well as complications. We go on to discuss the case in the light of a literature review. The severity of the elevation of the parathyroid hormone, other biochemical alterations, the presence of skeletal and renal complications and of a neck mass should alert the clinician to a possible parathyroid carcinoma. Radical surgery is the only effective therapy for parathyroid carcinoma, and should always be performed if a preoperative suspicion is entertained.