A differential diagnosis for hyperparathyroidism includes all causes of hypercalcemia; the primary causes of which are primary hyperparathyroidism and humoral hypercalcemia of malignancy. Benign familial hypocalciuric hypercalcemia is a rare condition of primary importance because failure to recognize this entity leads to unnecessary surgery. There are a plethora of other rare causes of hypercalcemia that can be distinguished from primary hyperparathyroidism by history and laboratory profiles. This article discusses the main and less common causes of hypercalcemia and provides guidance for distinguishing among them.