Background & aims: This study investigated the effects of nutritional support on postoperative complications, in relation with demographic and nutritional. factors, intraoperative factors, type and routes of nutritional regimens. Methods: A series of 1410 subjects underwent major abdominal surgery for gastrointestinal cancer and received various types of nutritional support: standard intravenous fluids (SIF; n = 149), total parenteral. nutrition (TPN; n = 368), enteral nutrition (EN; n = 393), and immune-enhancing enteral nutrition (IEEN; n = 500). Postoperative complications, considered as major (if lethal or requiring re-operation, or transfer to intensive care unit), or otherwise minor, were recorded. Results: Major and minor complications occurred in 101 (7.2%) and 446 (31.6%) patients, respectively. Factors correlated with postoperative complications at multivariate analysis were pancreatic surgery, (p < 0.001), advanced age (p = 0.002), weight toss (p = 0.019), low serum albumin (p = 0.019) and nutritional support (p = 0.001). Nutritional support reduced morbidity versus SIF with an increasing protective effect of TPN, EN, and IEEN. This effect remained valid regardless the severity of risk factors identified at the multivariate analysis and it was more evident by considering infectious complications only. Conclusions: Pancreatic surgery, advanced age, weight loss and low serum albumin are independent risk factors for the onset of postoperative complications. Nutritional support, particularly IEEN, significantly reduced postoperative morbidity. (C) 2007 Published by Elsevier Ltd.