Abdominal aortic aneurysms (AAAs) are dilations of the aorta to a transverse diameter of 3 cm or greater. Although 75% remain asymptomatic, the natural history of AAAs is to grow gradually at the rate of 0.25–0.5 cm a year, with an increasing risk of rupture and death as their transverse diameter increases.

Abdominal aortic aneurysms are predominantly a disease of advanced age, with prevalence from 3–10% among Western populations over the age of 50 years; they are rarely responsible for death below the age of 55 years. Due to the implementation of screening programs and the advent of endovascular repair, annual deaths due to AAAs in the USA have decreased, in spite of the fact that the population aged ≥ 50 years increased by over 12 million (20%) in the same time period.

Additional risk factors for AAA include smoking, male sex, atherosclerosis, and a family history of aneurysms. There may be an association with inguinal hernias. Abdominal aortic aneurysms occur less frequently in females, African Americans, and diabetics.

The risk of rupture is closely related to maximal transverse diameter. The annual rupture rate for untreated aneurysms is 0.5–5% for a diameter of 4–4.9 cm, 3–15% for 5–5.9 cm, 10–20% for 6–6.9 cm, 20–40% for 7–7.9 cm, and 30–50% for greater than 8 cm. For patients with aneurysms of the same diameter, rupture risk is greater in females, current smokers, cardiac and renal transplant recipients, and those with hypertension or decreased forced expiratory volume (FEV1).