Fever is common after a surgical procedure, occurring in 50% of patients. The appearance of postoperative fever is not limited to specific types of surgery: fever may occur after tonsillectomy in children, coronary artery bypass graft (CABG) surgery in elderly adults, gynecologic surgery, vascular surgery, or major abdominal surgery. Fever can occur immediately after surgery and seem to be related directly to the operation or may occur sometime after surgery as a result of an infection at the surgical site or infections that involve organs distant from the surgery. Often the specific cause of the fever is not found despite rigorous efforts to identify a cause.