 Water and electrolytic homeostasis is remarkably controlled by the mineralocorticoid pathway renin-angiotensin-aldosterone system acting on the renal tubule. However, the neonatal period in humans is characterized by a reduced ability of the kidney to ensure normal functions of urine concentration and maintenance of sodium and water balance. This renal functional immaturity, is associated in the very premature infants VPT born 32 weeks of amenorrhea SA to an immaturity of the adrenal responsible for a default of aldosterone biosynthesis . This relative aldosterone deficiency induces difficulties for VPT to adapt to extra-uterine life when maintaining a positive sodium balance is essential for postnatal growth. The improvement of perinatal care antenatal corticosteroids maturation, ventilation techniques and use of surfactant have increased the survival of these children . Nevertheless, extreme prematurity less than 32 weeks, which concerns nearly 2 of live births in France, remains associated with neurodevelopmental sequelae in nearly 40 of children at 5 years . 