Calcium is essential for homeostasis, and normocalcemia should be maintained strictly during the perioperative period. The biochemistry of calcium equilibrium results from the calcium-sensing receptors on the parathyroid glands, which detect changes in calcium concentrations and initiate the proper response. Asymptomatic hypercalcemia is a common metabolic derangement that is often discovered on routine serum screening. The most common etiologies are primary hyperparathyroidism and cancer. Increasingly, parathyroidectomy is the preferred therapy for primary hyperparathyroidism. Severe hypercalcemia ("hypercalcemic crisis") should be managed aggressively with a combination of intravenous fluids, steroids, bisphosphonates, and calcitonin. Some of these patients may require an urgent parathyroidectomy for calcium control. Hypocalcemia needs to be verified, as many cases of hypocalcemia are the artifact of hypoalbuminemia. Severe hypocalcemia occurs after subtotal or total parathyroidectomy with auto transplantation as well as after massive resuscitation or blood transfusion. Strategies aimed at correcting calcium concentrations depend on the severity of symptomatology. If symptoms are mild, oral calcium supplementation can be given; otherwise, intravenous calcium should be administered.