Milk-alkali syndrome can be caused by ingesting large amounts of calcium carbonate. Coincident with the promotion of calcium carbonate as treatment for both dyspepsia and osteoporosis, milk-alkali syndrome is now a common cause of hypercalcemia severe enough to require admission to the hospital. The syndrome accounted for less than 2% of such admissions before 1990, but from 1990 through 1993, it was the cause of hypercalcemia for over 12% of these patients. Only primary hyperparathyroidism and hypercalcemia of malignancy (excluding multiple myeloma) are more common. The diagnosis of milk-alkali syndrome is made almost entirely based on the patient's history; careful attention to dietary practices and over-the-counter drug use is required, as numerous over-the-counter medications contain calcium carbonate. Modern assays for PTH demonstrate the expected suppression of PTH by hypercalcemia. Nonetheless, measurement of PTH must be performed in a timely manner as treatment with intravenous saline may result in hypocalcemia and elevated PTH soon after admission. Given the pathophysiology of milk-alkali syndrome compared to other causes of hypercalcemia, hypocalcemia with rebound hyperparathyroidism is probably unique to milk-alkali syndrome.