Hypocalcemia is often clinical problem. The levels of total serum calcium below 2.15 mmol/L (<8.6 mg/dl) and ionized calcium below 1.15 mmol/L (4.6 mg/dl) are considered to be consistent with hypocalcemia. The major factor that influence the hypocalcemia is low parathyroid hormone. Clinical manifestations are different: ranging from few, if any, in case of mild hypocalcemia, to life-threatening, when hypocalcemia is severe or acute. Classic clinical manifestation is tetany: open or latent. The treatment varies with its severity and the underlying cause. Recommendations contains the administration of calcium and vitamin D.