It is increasingly evident that many disorders common in the aging individual may be accompanied by disturbances of fluid and sodium balance, especially hyponatremia. Physiological alterations in water and sodium regulation have been identified as part of the normal aging process which may contribute to the relative frequency of fluid and electrolyte disorders in the elderly. Hyponatremia may present with a wide variety of symptoms and may be a clue to the existence of an underlying major disease process. Treatment involves both acute and long-term management based on identification of the causative disorder and understanding of the pathophysiologic mechanism which has led to development of hyponatremia.