Hypernatremia, defined as a serum sodium concentration greater than 145 mmol/l, is an electrolyte disorder associated with increased in-hospital morbidity and mortality. Its prevalence is estimated between 1 to 3% in hospitalized patients and up to 11% in intensive care. It most often results from an impaired thirst mechanism or the inability to access water to drink. The clinical presentation varies depending on the severity of the hypernatremia. Patients may be pauci-symptomatic to comatose. Correcting too quickly the hypernatremia can lead to serious consequences (cerebral hemorrhage, demyelination). Prevention of the onset of hypernatremia is essential in the hospital. Its management consists of treating the underlying cause and correcting the hyperosmolarity by ensuring close monitoring of the sodium level.