Nonketotic hypertonicity (NKH) is one of the most common endocrine emergencies. It is more common in the elderly patient with noninsulin-dependent diabetes mellitus but may occur in insulin-dependent diabetes as well. Although there are many possible precipitating causes, the final common pathway is usually decreased access to water. Treatment consists of vigorous hydration, electrolyte replacement, and small amounts of insulin. Most deaths from NKH occur in the first 2 days of hospitalization; therefore, a significant decrease in morbidity and mortality can be expected by education of patients and their caregivers in the prevention of NKH.