Hyponatremia is very frequent in neonates, especially in VLBW. Recent data have shown that hyponatremia is not so benign as previously believed,and several clinical studies have indicated that preterms with mild to moderate chronic hyponatremia may experience poor growth and development retardation. The aim of this review is to present how to differentiate hypovolemic, euvolemic and hypervolemic hypernatremias, suggesting algorithms for practical management.