BACKGROUND The aim of this study was to determine the accuracy of prediction of the surgeon's 'gut-feeling' in estimating postoperative outcome. METHODS A prospective series of 1077 consecutive patients undergoing major hepatobiliary or gastrointestinal surgery were studied. Patients having elective (n = 827) and emergency (n = 250) procedures were included. The surgeon predicted the development of postoperative complications immediately after completion of surgery on a scale from 0 to 100 percent. These predictions were compared with the actual outcome and with predictions made using the Physiological and Operative Severity Score for the enUmeration of Mortality and morbidity (POSSUM). The Portsmouth predictor equation (P-POSSUM) was applied for the estimation of mortality. RESULTS The observed morbidity and mortality rates were 29.5 and 3.4 percent respectively. POSSUM predicted a morbidity rate of 46.4 percent and P-POSSUM a mortality rate of 6.9 percent. The surgeon's gut-feeling was more accurate in the prediction of morbidity at 32.1 percent. On the basis of gut-feeling, surgeons overpredicted morbidity in elective surgery, but underestimated the risk of complications in the emergency setting. The (P)-POSSUM scoring system overpredicted morbidity and mortality for elective and emergency operations. CONCLUSIONS The surgeon's gut-feeling is a good predictor of postoperative outcome, especially after elective surgery. (P)-POSSUM overpredicted morbidity and mortality in this series of major gastrointestinal and hepatobiliary operations.