Hyponatremia, characterized by low serum sodium and hypoosmolality, commonly results from excess water relative to sodium, often due to conditions like syndrome of inappropriate antidiuretic hormone secretion, dehydration, or fluid shifts. Accurate diagnosis involves assessing serum and urine parameters alongside volume status. Treatment emphasizes identifying and addressing underlying causes, restricting fluid intake, and gradually correcting sodium concentration to prevent neurologic complications such as brain edema. While sodium deficits are rarely calculated, they may be needed in specific cases like cerebral salt wasting. Effective management relies on comprehensive history, physical examination, laboratory testing, and careful monitoring to ensure optimal patient outcomes.