Many animals with diabetes mellitus are severely ill on clinical presentation. The spectrum of disease is quite variable and includes diabetic ketoacidosis (DKA), ketosis without acidosis, hyperosmolar nonketotic syndrome (HNKS), and other nonketotic variants (negative urine ketones, serum osmolality < 340 mOsm/kg with or without acidosis). These more severe forms of diabetes are often precipitated by concurrent diseases such as pyelonephritis, pancreatitis, pyometra, hyperadrenocorticism, renal failure, and heart failure. To make matters worse, in-hospital treatment of diabetic dogs and cats is commonly associated with serious complications, including hypoglycemia, hypokalemia, and hypophosphatemia.