BACKGROUND The Physiological and Operative Severity Score for the enUmeration of Mortality and morbidity (POSSUM) is an objective and appropriate scoring system for risk-adjusted comparative general surgical audit. This score was devised in the UK and has been used widely, but application of POSSUM to centres outside the UK has been limited, especially in developing countries. This prospective study validated its application in a surgical practice with a different population and level of resources. METHODS All general surgical patients who were operated on under regional or general anaesthesia as inpatients over a 4-month period at Sarawak General Hospital in 1999 were entered into the study. All data (12 physiological and six operative factors) were analysed for mortality only with the POSSUM equation and the modified Portsmouth POSSUM (P-POSSUM) equation. Comparisons were made between predicted and observed mortality rates according to four groups of risk: 0-4, 5-14, 15-49 and 50 per cent or more using the 'linear' method of analysis. RESULTS There were 605 patients who satisfied the criteria for the study. Some 56.7 per cent of patients were in the lowest risk group. The POSSUM predictor equation significantly overestimated the mortality in this group, by a factor of 9.3. The overall observed mortality rate was 6.1 per cent and, again, the POSSUM predictor equation overestimated it at 10.5 per cent (P < 0.01). In contrast, the observed and predicted mortality rates for all risk groups, including the predicted overall mortality rate of 4.8 per cent, were comparable when the P-POSSUM predictor equation was used. CONCLUSION The POSSUM scoring system with the modified P-POSSUM predictor equation for mortality was applicable in Malaysia, a developing country, for risk-adjusted surgical audit. This scoring system may serve as a useful comparative audit tool for surgical practice in many geographical locations.