During 8 years of an ultrasound screening programme for abdominal aortic aneurysm (AAA), 8944 people aged 65-80 years were scanned. 356 (4%) had AAA of diameter 3 cm or greater. Under our criteria repair was indicated if the aortic diameter reached 6 cm, if expansion reached 1 cm per year, or if the AAA caused symptoms; 124 patients met these criteria. Among the 8820 screened patients who did not meet the criteria, 1 death (0.4%) was attributed to ruptured aneurysm, although the retroperitoneal haematoma had developed within 5 days of surgery for a colon tumour. The risk of aortic rupture in patients with AAA less than 6 cm diameter with these criteria (0.4%) is lower than that for elective surgery (1-8%). Surgical repair is unnecessary and possibly detrimental in such patients, provided that ultrasound surveillance is undertaken.