The syndrome of inappropriate antidiuretic hormone secretion (SIADH) is caused by an incapacity of plasmatic hypotonia to inhibit antidiuretic hormone (ADH) secretion. This phenomenon leads to a water retention and an expanded extracellular fluid volume, and secondary to a dilution of plasmatic sodium and also to a renal loss of sodium. The SIADH is a relatively rare syndrome, which may occur in various circumstances: central nervous system diseases, cancers, infections... Sometimes, it may be observed as a drug-related side effect: carbamazepine, chlorpropamide, antidepressors, anticancer drugs are particularly involved.