Introduction: Postoperative complications after major upper gastrointestinal surgery can be devastating. Malnutrition has been found to be an important risk factor for postoperative complications. However, attempts at trying to detect malnourished patients preoperatively can be cumbersome and complex and are often not done. One simplified way of assessing nutritional status is the ANS system. The aim of this study was to show the relationship between ANS score and the postoperative outcome. Methodology: Medical record of all patients undergoing major EG and HB surgeries at Concord Hospital between 2010 and 2012 were retrospectively analysed. Results: 83 patients were operated and included (1) Whipples' procedure (20.5%), (2) total/subtotal gastrectomy (44.6%), (3) Ivor-Lewis esophagectomy (18%), and (4) distal pancreatectomy (14.5%). The mean ANS score was 1.58. Patients with higher ANS score (2 or more) were found to have significantly higher rates of wound infection (41% vs 12%, p<0.002), anastomotic leaks (13.7% vs 1.92%, p=0.034), unexpected return to operating theatre (31% vs 3.9%, p<0.001), slower return of bowel function as compared to patients with low ANS score (0 or 1). Conclusion: This study demonstrates the importance of screening for malnourished patients prior to their operation. Given its simplicity and effective predictive value, we recommend use of ANS system.