Calcium plays a critical role in neuromuscular excitement and other cellular functions. Therefore, extracellular calcium concentration is maintained within a very narrow range through interaction of calcium regulating hormones such as parathyroid hormone, calcitonin, and vitamin D. Thus, symptomatic severe hypercalcemia has rarely occurred in a clinical situation, particularly in patients with hypoparathyroidism. In general, a large amount of calcium and vitamin D should be supplied in order to avoid hypocalcemia in hypoparathyroid patients. A 63-year old female patient was admitted suffering from nausea, vomiting, and weakness for two weeks. She had a history of total thyroidectomy and subsequent permanent hypoparathyroidism and long-term calcium and vitamin D supplementation. For over 10 years she had not changed her daily amount of calcium and vitamin D intake. Her initial serum calcium was 17.5 mg/dL, creatinine was 2.57 mg/dL, and total CO2 was 33.1 meq/L. After thorough examination, we concluded that milk-alkali syndrome was the cause of severe hypercalcemia. Therefore, special pay attention should be paid to aged patients on calcium supplementation in situations of increased risk of dehydration and renal insufficiency, even though the usual amount of calcium intake was unchanged for several years.