Diuretics are medications that promote the excretion of water and electrolytes. They are primarily used in the management and treatment of states of inappropriate salt and water retention. Diuretics represent one of the most common classes of drugs administered to sick neonates, the more so in very low birth weight infants. Diuretic drugs, especially loop diuretics, are often administered in the neonatal intensive care unit as off-label medications. This is the case for a variety of clinical situations, in which an increase in sodium excretion is not the primary goal of treatment (transitory tachypnoea of the newborn at term, hyaline membrane disease, patent ductus arteriosus of preterm infants). Thiazides and furosemide are widely used to treat preterm infants with oxygen-dependent chronic lung disease, despite a lack of data on beneficial effect of long-term therapy on pulmonary function or clinical outcome. This article reviews the mechanism of action, indications, administration, posology, adverse effects and contraindications of diuretics in newborn infants. Based on the most recent information available in the literature, we will discuss data supporting (or questioning) the use of diuretic in specific neonatal diseases. Research priorities over this issue will be briefly presented.