Despite many advances in the overall treatment of type I diabetes mellitus during the last few years, no major advance has been made in decreasing the mortality rate of diabetic ketoacidosis or hyperosmolar hyperglycemic nonketotic coma. A major concern in both of these disease states is the development of cerebral edema during treatment. The guiding principles of therapy in both disease states are rehydration, electrolyte replacement, insulin therapy, and treatment of any underlying illnesses. If the patient is hypotensive, therapy begins with colloid or normal saline administration to support blood pressure. Fluid and electrolyte deficits should be calculated and replaced during 48 hours. Low-dose insulin therapy is employed for treatment of hyperglycemia. Neurologic function should be carefully monitored and mannitol administered if a change in neurologic function occurs.