BACKGROUND: Endovascular techniques are gaining acceptance as minimally invasive methods for abdominal aortic aneurysm repair, although there have been few studies that provide direct comparison with conventional techniques. A prospective study that compares morbidity and mortality rates following abdominal aortic aneurysm repair, using a physiological scoring system, is presented. METHODS: Between December 1994 and November 1997, 104 elective open aneurysm repairs and 49 endovascular aneurysm repairs were performed at this institution. These patient cohorts were compared using the Portsmouth predictor equation scoring system, which has been shown to predict outcome in vascular surgery. Prospective data from patient notes were used to obtain physiological and operative severity scores that were analysed to predict expected (E) to observed (O) mortality and morbidity rates. RESULTS: Although physiological variables were equivalent in both groups, conventional surgery had a higher mortality (P < 0.05) and morbidity (P < 0.001) rate than endovascular surgery, which was related to the operative severity scores. CONCLUSION: These data suggest that open aortic aneurysm repair has a higher operative severity than endovascular repair which may be reflected in increased mortality rates.