A series of 245 patients was operated upon for abdominal aortic aneurysm during the years 1969-77, of whom 162 were elective cases while in 83 the aneurysm was leaking or had ruptured. The hospital mortality for the latter group fell from 77 per cent at the beginning of the study period to 30 per cent at the end. For elective operations, hospital mortality averaged 9.3 per cent, though during the last 2 years there were no deaths in the 51 consecutive cases. Operative methods and postoperative treatment changed during the years of the study, with few excision-replacement grafts and greater use of the inlay technique, most of the latter being simple unbranched Dacron tubes. Early graft infection, the most important and serious surgical complication, caused 9 deaths, an overall incidence of 3.7 per cent, of which 8 were in patients who received no perioperative antibiotics and only 1 among the patients who did receive them. All deaths were in the inlay group. The reasons for this are discussed. Since July 1976 perioperative antibiotic treatment has been routine for all arterial prosthetic graft patients in our hospital.