An abdominal aortic aneurysm was detected in 77 patients among 16 488 abdominal ultrasonographies (US) performed in 1978-1983. In 62 cases the US finding was confirmed by operation, autopsy or other imaging method, and the US finding proved true in 60 cases. The length and diameter were accurately estimated and accompanying thrombosis reliably visualised. An error rate of 24% was observed in assessing the relation of the aneurysm to the renal arteries. US is recommended as the primary imaging mode in suspected abdominal aortic aneurysm. Screening of the abdominal aorta is recommended in elderly patients with abdominal pain and/or referred for abdominal US.