Ultrasound is a useful modality to determine the maximum diameter of an abdominal aortic aneurysm (AAA) as it relates to the indications for repair at presentation or in long-term surveillance. Two-dimensional (2D) ultrasound has traditionally been used for the initial diagnosis and long-term surveillance of AAAs in order to avoid the radiation exposure and cost of computed tomography (CT). Three-dimensional (3D) ultrasound, which captures aneurysm diameter and volume, may be a more accurate tool to evaluate AAAs. This chapter will describe the role of 3D ultrasound in the diagnosis and surveillance of AAAs and in the surveillance following endovascular aneurysm repair.