Hypoglycemia is the most common endocrine medical emergency. Because the brain has an obligatory need for contiunous inflow of glucose, any interruption to that supply puts the individual at risk for neuroglycopenia. The latter impairs brain function and precludes self-administered corrective treatment. Treatment of hypoglycemia, especially in those patients with diabetes mellitus, involves punctilious attention to preventive measures. The acute event, if recognized, requires treatment with oral ingestion of free carbohydrate. Neuroglycopenia can be treated equally effectively with intravenous glucose or parenteral glucagon administration.