An abdominal aortic aneurysm (AAA) is a permanent dilation of the abdominal aorta to a diameter of 3 cm or greater (or 1.5 times the normal adjacent aortic diameter). AAA screening ultrasound is recommended for men aged 65–75 who have ever smoked. The anteroposterior (AP) diameter is the key measurement, taken in the transverse plane from outer wall to outer wall. An AAA of 5.5 cm or greater in men (5.0 cm in women) is generally considered the threshold for surgical repair due to increasing rupture risk.