Malnutrition has been shown to have an adverse effect on the clinical outcome of surgical patients. During the past 25 years, investigators have sought to determine whether clinical outcome can be improved by the administration of pre- or postoperative (perioperative) nutritional support. We conclude that the clinical outcome of severely malnourished surgical patients is improved by perioperative nutritional support and that this should be administered whenever possible via the enteral route. The clinical outcome of less severely malnourished surgical patients, including those who are normally nourished, can be improved by the administration of oral dietary supplements at a time in the postoperative period when patients are ingesting free fluids. Some of these patients may also benefit from early postoperative enteral tube feeding, but further work is required to determine the effects following different types of surgery before this is adopted for routine use. Parenteral nutrition is only indicated in the postoperative period when major complications occur in association with intestinal failure.