Hyperparathyroid crisis is a rare disease but should be suspected in acutely ill patients complaining of weakness, lethargy, nausea, vomiting, confusion and abdominal pain. Despite the variety of clinical manifestations, the syndrome forms a distinctive pattern which, in the presence of a serum calcium level greater than 16 mg/100 ml, should be recognized. The most difficult problem in diagnosis is the differentiation of hyperparathyroid crisis from ectopic parathyroid hormone-producing tumors. The disease is an endocrine emergency which requires prompt surgery after rapid correction of dehydration and hypercalcemia. The best results are achieved by removing offending parathyroid tissue within 72 hours after the onset of symptoms.