Hyponatremia and hypernatremia are common findings in the inpatient and outpatient settings. Sodium disorders are associated with an increased risk of morbidity and mortality. Plasma osmolality plays a critical role in the pathophysiology and treatment of sodium disorders. Hyponatremia and hypernatremia are classified based on volume status (hypovolemia, euvolemia, and hypervolemia). Sodium disorders are diagnosed by findings from the history, physical examination, laboratory studies, and evaluation of volume status. Treatment is based on symptoms and underlying causes. In general, hyponatremia is treated with fluid restriction (in the setting of euvolemia), isotonic saline (in hypovolemia), and diuresis (in hypervolemia). A combination of these therapies may be needed based on the presentation. Hypertonic saline is used to treat severe symptomatic hyponatremia. Medications such as vaptans may have a role in the treatment of euvolemic and hypervolemic hyponatremia. The treatment of hypernatremia involves correcting the underlying cause and correcting the free water deficit.