The usual treatment of diabetic patients during surgery with general anesthesia owes little to logic, common sense, or knowledge of requirements, and mortality and morbidity remain high in many centers. In the nondiabetic patient, surgery is accompanied by a rise in secretion of catabolic hormones, insulin-resistance and loss of protein. Therapy of the diabetic patient should be designed to account for these changes and to avoid hypoglycemia, hyperglycemia, and hyperketonemia. It is suggested that for major operations for well-controlled non-insulin-dependent diabetic (NIDDM) persons and for all minor and major operations for insulin-dependent diabetic (IDDM) persons and poorly controlled NIDDM, a combined insulin (3.2 U/h), glucose (10 g 10% dextrose/h), and potassium infusion should be used until oral feeding recommences. The insulin dose should be modified periodically according to bedside glucose monitoring. Fluids should be used as in nondiabetic patients, except that lactate-containing solutions should be avoided. Insulin requirements will be increased (1) by infection, (2) in patients with hepatic disease, (3) in obese patients, (4) in steroid-treated patients, and (5) during cardiovascular surgery. A diabetes-care team should preferably be responsible for the care of the diabetic pre-, per-, and postoperatively.