An ultrasonography screening programme for detecting abdominal aortic aneurysm (AAA) in the community is described in which 7200 men and women aged between 65 and 80 years were contacted by letter. Of these, 4237 were screened; the aorta was visualized in 4122 and 179 AAAs of 3 cm or more in diameter were detected (4.3 per cent). Criteria for surgery are suggested and the results of their application prospectively over 6 years are discussed. Using these criteria, under 10 per cent of patients with ultrasonographically-detected AAA should require surgery for this condition provided ultrasonography follow-up is used.