Comparison of outcome after colorectal resection between different surgical units is difficult. Crude rates of morbidity and mortality may give a distorted picture as such rates fail to account for variations in case mix and physiological status of patients. The simple and validated scoring system POSSUM (Physiological and Operative Severity Score for enUmeration of Mortality and morbidity) was used to compare outcome after colorectal resection in two units. Consecutive series of patients who underwent colorectal resection in unit 1 (a university teaching hospital) or unit 2 (a district general hospital) were scored with the POSSUM system. Postoperative complications and 30-day mortality were recorded. In unit 1, 66 patients underwent colorectal resection with a mortality rate of 6 per cent and a morbidity rate of 9 per cent. In unit 2 the rates of mortality and morbidity were 9 and 26 per cent respectively for 182 patients undergoing colorectal resection. However, application of POSSUM predicted a mortality rate of 5.2 per cent for patients in unit 1 and 9.8 per cent for those in unit 2 with predicted morbidity rates of 11.2 and 23.9 per cent respectively. Direct comparison of outcome between these two units would be misleading. Application of POSSUM allows more realistic comparative audit of colorectal resection.