Disorders in serum sodium, hyponatremia and hypernatremia, are frequently encountered in both inpatient and outpatient settings. Many sodium disorders are iatrogenic, caused by inappropriate intravenous fluid management. The methods of prevention and treatment of serum disorders differ based on the underlying disease states. Nine cases are presented to illustrate different aspects of fluid management, with an emphasis on the prevention and treatment of disorders in serum sodium. Key concepts that are discussed are (1) when to use an isotonic fluid versus a hypotonic fluid, (2) when to restrict or liberalize maintenance intravenous fluids, (3) how to use 3% sodium chloride for the treatment of hyponatremic encephalopathy, (4) when to use desmospressin to prevent the overcorrection of chronic hyponatremia, and (5) strategies to treat different causes of hypernatremic dehydration in children.