Disorders of calcium homeostasis are frequent and seldom diagnosed in the Emergency Department. In both the adult and pediatric population, the causes of increased or decreased calcium are many, and the index of suspicion needs to be raised for these disorders. Selective ordering is warranted for patients with altered mental status, seizures, neuromuscular irritability, or in patients with diseases known to have abnormalities of calcium as a complicating factor. These include renal failure, multiple myeloma, metastatic cancer, granulomatous disease, and endocrinopathies.