Too often neglected, dosage of phosphatemia should yet be kept on mind. The role of phosphorus in bone mineralization and regulation of acid-base balance is well known. Phosphorus is also an energy purveyor during numerous biologic reactions, and deep deprivation may lead to a lot of pathologic situations, sometimes severe. Mild hypophosphatemia is not rare and occurs in various clinical or therapeutic circumstances; deep hypophosphatemia is rather uncommon, occuring chiefly during hyperalimentation or realimentation of starving patients, especially alcoholics. Deep hypophosphatemia (by depletion or transfer) mainly induces clinical and pathological manifestations; they are subsequent to alterations of glucose metabolism, leading to a failure in ATP and 2,3 DPG synthesis. These metabolic events particularly explain muscular and hematological manifestations of hypophosphatemia. Phosphorus loading per os, or in severe cases intravenously corrects the biological abnormalities and improves clinical manifestations.