Hypernatremia is defined as a plasma sodium concentration greater than 145meq/liter. This is primarily due to water loss in adults although increased salt ingestion may be a cause for it. When plasma sodium concentration rises above 145meq/liter, thirst is stimulated, this results in ingestion of water. Hypothalamic osmoreceptors cause synthesis and release of an antidiuretic hormone. Normal renal response causes reabsorption that prevents further loss of water. These normal physiological responses help bring plasma sodium back to normal. Persistent hypernatremia, therefore, implies an inability to sense thirst or lack of access to water, since ingestion of water will prevent development of significant hypernatremia even in the absence of antidiuretic hormone release or lack of renal response to its effect. Elderly persons have decreased thirst, and therefore, ingest less amounts of water than their younger counterparts. Hospitalized elderly patients and frail nursing home residents are at an increased risk for the development of hypernatremia because they rely on others for their water needs. Therefore, adequate water must be prescribed and given to these individuals. In this article, we review the risk factors, pathophysiology, causes, prevention, and management of hypernatremia in the elderly.