Hypercalcemia of acute bone atrophy is a rare metabolic disorder, most common in adolescence, following immobilization. The symptoms involve almost every organ system, making the diagnosis difficult, not only because of the rarity of the syndrome but also because of the protean nature of the symptoms. Treatment consists in decreasing calcium ingestion, decreasing calcium absorption, promoting calcium diuresis, and preventing liberation of calcium from the skeletal system. A low-calcium diet, the temporary use of corticosteroid drugs, adequate parenteral fluids, and mobilization of the patient are all measures useful to accomplish this end. Parathyroid exploration is unnecessary. Although diagnosis may be difficult, adequate treatment, once instituted, is effective.