Purpose of the review: To outline recent findings concerning the efficacy of immunonutrients in patients undergoing surgery. Recent findings: Surgery induces an inflammatory response that can become excessive and damaging in some patients. The major risk factors are pre-existing nutritional status and increasing levels of surgical stress. A range of nutrients, including several amino acids, antioxidant vitamins and minerals, ω-3 fatty acids, and nucleotides, are able to modulate inflammation and the associated oxidative stress, and maintain or improve immune function. Considering the overall treatment effect of immune-modulating nutrients, parenteral glutamine is recommended in patients receiving parenteral nutrition, while enteral glutamine should be considered for burn and trauma patients. Antioxidants, particularly selenium, should be considered for critically ill patients, and enteral formulas enriched with fish oils are recommended for patients with acute respiratory distress syndrome. Arginine-supplemented diets are not recommended. In summary, malnourished patients should receive preoperative artificial nutrition for at least 10 days prior to major surgery and for 7 days postoperatively. Enteral nutrition is the best support for these patients. The benefit of immuneenhancing diets in severely malnourished patients remains to be proven. Preoperative oral immunonutrition (arginine, omega-3 fatty acids, and nucleotides) is indicated for non-malnourished patients. Although patients with cancer exhibit some special metabolic features, preoperative immunonutrition is also indicated. Summary: Immunonutrition is effective in improving outcome in a wide range of patients, particularly in malnourished individuals. However, further research using larger, better-designed trials is needed to assess whether immune function is benefited, with an improved clinical outcome in vulnerable patients.