Inadequate treatment of severe hyponatremia (<120 mEq/L) can be associated with severe neurological damage. In acute (<48 hours) hyponatremia, usually observed in the postoperative period, prompt treatment with hypertonic saline (3%) can prevent seizures and respiratory arrest. For patients with chronic (>48–72 hours) symptomatic hyponatremia, correction must be rapid during the first few hours (to decrease brain edema) followed by a slow correction limited to 10 mmol/L over 24 hours to avoid the development of osmotic demyelinating syndrome. In patients with asymptomatic hyponatremia, slow correction is the appropriate approach. When patients are overtreated, neurologic damage can be prevented by relowering the serum sodium (SNa) so that the daily increase in SNa remains below 10 mmol/L/24 hours. Frequent measurements of SNa during the correction phase of SNa are mandatory to avoid overcorrection. The use of urea to treat hyponatremia represents an advantageous alternative to hypertonic saline.