Elevated calcium levels in the blood or serum can result from many disease processes, and requires careful investigation. Hyperparathyroidism, and Hypercalcemia associated with malignancy constitute the majority of cases of Hypercalcemia. These two entities are differentiated by a high intact PTH level in hyperparathyroidism, and a suppressed PTH level in hyperparathyroidism associated with malignancy. A number of drugs can produce elevated calcium level, including antacids, lithium, thiazide diuretics, vitamin A (including retinoids used to treat acne) intoxication, and vitamin D intoxication. Granulomatous diseases such as sarcoid and tuberculosis can also produce Hypercalcemia. Other endocrine abnormalities including acromegaly, hyperparathyroidism, adrenal insufficiency, and pheochromocytoma can cause it as well. Prolonged immobilization can also produce Hypercalcemia. An uncommon entity that mimics hyperparathyroidism is benign familial hypocalciuric hypercalcemia. This entity has normal or elevated PTH in the face of elevated calcium. Measurement of 24 hour urine calcium excretion reveals abnormally low calcium excretion. It is important to exclude this entity, as failure to recognize it can result in unnecessary surgery.