The patients with diabetes are treated with a variety of regimens and are scheduled for surgery at varying times of the day, there is no established consensus for optimal preoperative management. Perioperative glycemic control has a significant impact on the risk of infectious complications - including pneumonia, wound infection, urinary tract infection and sepsis - in patients with diabetes undergoing a variety of surgical procedures. Therefore, the goal of preoperative glycemic control is to avoid hypoglycemia, excessive hyperglycemia, lipolysis, protein catabolism, electrolyte disturbance and ketoacidosis. However, the effects of preoperative glycemic control are not definitive. Patients with type 1 diabetes should receive insulin replacement, while those with type 2 diabetes may need to discontinue oral medications prior to surgery and might require insulin therapy to maintain blood glucose control. The actual treatment should be individualized for each patient, based on diabetes classification, usual diabetes regimen, state of glycemic control, and extent of the surgical procedure. Medical judgment should override these recommendations as needed. Whenever possible, metabolic abnormalities should be corrected, and surgery should be scheduled early in the day.