The goal of this study was to validate the usefulness of risk assessment scoring systems for a surgical audit in elective digestive surgery for elderly patients. The validated scoring systems used were the Physiological and Operative Severity Score for enUmeration of Mortality and morbidity (POSSUM) and the Portsmouth predictor equation for mortality (P-POSSUM). This study involved 153 consecutive patients aged 75 years and older who underwent elective gastric or colorectal surgery between July 2004 and June 2006. A retrospective analysis was performed on data collected prior to each surgery. The predicted mortality and morbidity risks were calculated using each of the scoring systems and were used to obtain the observed/predicted (O/E) mortality and morbidity ratios. New logistic regression equations for morbidity and mortality were then calculated using the scores from the POSSUM system and applied retrospectively. The O/E ratio for morbidity obtained from POSSUM score was 0.23. The O/E ratios for mortality from the POSSUM score and the P-POSSUM were 0.15 and 0.38, respectively. Utilizing the new equations using scores from the POSSUM, the O/E ratio increased to 0.88. Both the POSSUM and P-POSSUM over-predicted the morbidity and mortality in elective gastrointestinal surgery for malignant tumors in elderly patients. However, if a surgical unit makes appropriate calculations using its own patient series and updates these equations, the POSSUM system can be useful in the risk assessment for surgery in elderly patients.