Diabetic ketoacidosis (DKA) and hyperosmolar hyperglycemic state (HHS) are the two most acute life-threatening complications of diabetes mellitus and in most cases treatment should be administered in an intensive care unit. Clinically, DKA and HHS differ according to the presence of metabolic acidosis; however, the treatment of DKA and HHS is similar. The main principles are intravenous administration of insulin and correction of fluid and electrolyte abnormalities which are typically present. By the application of a standardized treatment algorithm a low mortality rate can be achieved.