Abdominal aortic aneurysms (AAAs) occur in 1 of 20 older men, remain asymptomatic for many years, and, if left untreated, cause death from rupture in about one third of patients. Ultrasonography is a suitable screening test for AAA, and elective repair can prevent rupture. Although these features suggest a promising target for a screening program, evidence of benefit from AAA screening has only recently become available. Four randomized trials of ultrasonographic screening involving more than 125 000 men have been reported, and each trial observed a reduction in AAA-related mortality (which was statistically significant in 2 trials), ranging from 21% to 68%. One trial in women found no benefit. Other studies indicate that screening can begin in men older than 65 years of age and does not need to be repeated if results are negative. An AAA larger than 5.5 cm in diameter should be considered for elective open or endovascular repair. Most aneurysms detected at screening are smaller and should be kept under surveillance with periodic imaging measurement. Widespread elective repair of small AAAs could reduce the benefits and increase the costs of screening. No medical treatments have been proven to reduce the enlargement rate. If elective repair is reserved for larger AAAs, one-time ultrasonographic screening for AAA can be recommended for men 65 to 79 years of age who have ever smoked [correction].