The abdominal aorta is the largest artery in your abdomen, running from your diaphragm down to roughly your belly button, where it splits into two smaller arteries that supply your legs. It’s the continuation of the aorta after it exits your chest, and its job is to deliver oxygen-rich blood to nearly every organ below your ribcage, including your kidneys, liver, stomach, intestines, and reproductive organs.
Where It Sits and How Big It Is
The abdominal aorta begins where the aorta passes through the diaphragm, at about the level of the 12th thoracic vertebra (the lowest part of your mid-back). It runs slightly left of your spine, traveling downward through the abdominal cavity until it splits into the two common iliac arteries near the fourth lumbar vertebra, roughly at the level of your navel.
In a healthy adult, the abdominal aorta is widest at the top and tapers as it descends. Men tend to have slightly larger aortas than women. At the upper end, the average diameter is about 22 to 23 mm in men and 19 to 20 mm in women. By the lower end, just before the split, it narrows to around 16 mm in men and 14 mm in women. These numbers vary somewhat by age, body size, and ethnicity, but across studies from the U.S., Europe, and Asia, the general pattern holds: roughly 15 to 22 mm from bottom to top.
What It Supplies
The abdominal aorta is essentially the main highway for blood flow to your lower body. Along its length, it sends out branches to specific organs and structures. These branches fall into two categories: unpaired arteries that go to single organs along the midline, and paired arteries that serve organs on both sides of the body.
The major unpaired branches, in order from top to bottom:
- Celiac trunk: feeds the stomach, liver, and spleen
- Superior mesenteric artery: supplies most of the small intestine and the first half of the large intestine
- Inferior mesenteric artery: supplies the remaining large intestine and rectum
The major paired branches include the renal arteries (which deliver blood to each kidney), the gonadal arteries (to the ovaries or testes), the adrenal arteries (to the adrenal glands sitting atop each kidney), and the lumbar arteries (to the muscles and spinal cord in the lower back). The inferior phrenic arteries, which supply the underside of the diaphragm, also branch off as a pair near the top.
At the very bottom, the abdominal aorta splits into the left and right common iliac arteries, which carry blood into the pelvis and legs. A small vessel called the median sacral artery continues straight down the midline to supply the tailbone area. Because so many critical organs depend on this single vessel, any disruption to blood flow through the abdominal aorta can have widespread consequences.
Abdominal Aortic Aneurysm
The most well-known condition affecting the abdominal aorta is an abdominal aortic aneurysm (AAA), a bulge in the artery wall where it has weakened and expanded. An aneurysm is formally defined as a diameter greater than 3 cm, or more than 50% larger than the normal width of a healthy aorta. Most aneurysms develop in the lower portion of the abdominal aorta, below where the renal arteries branch off.
AAAs typically grow slowly and produce no symptoms for years. Many people discover them incidentally during imaging for something else entirely. The danger lies in rupture: if an aneurysm expands enough, the thinned wall can tear open, causing massive internal bleeding. A ruptured AAA is a life-threatening emergency. Warning signs include sudden, severe pain in the abdomen or lower back, dizziness or fainting, a rapid heartbeat, clammy skin, and dangerously low blood pressure.
Who Is at Risk
Smoking is by far the strongest modifiable risk factor. A large UK study found that current smokers had more than four times the risk of developing an aortic aneurysm compared to people who never smoked. For abdominal aortic aneurysms specifically, that risk jumped to nearly nine times higher. Heavier smoking made things worse: people who smoked 20 or more cigarettes a day had close to six times the overall aneurysm risk compared to light smokers. Former smokers still carried about 70% more risk than never-smokers, though quitting clearly helped.
Other significant risk factors include older age, male sex, and having a first-degree relative (parent or sibling) with an AAA. Atherosclerosis, the buildup of fatty deposits in artery walls, also plays a role. When atherosclerosis affects the renal arteries branching off the abdominal aorta, it can contribute to chronic kidney disease and high blood pressure that’s resistant to medication.
Screening Recommendations
Because AAAs are silent until they’re dangerous, screening focuses on the groups most likely to benefit. The U.S. Preventive Services Task Force recommends a one-time ultrasound screening for men aged 65 to 75 who have ever smoked (defined as 100 or more cigarettes in a lifetime). For men in that age range who have never smoked, screening is offered selectively based on individual risk. The Society for Vascular Surgery goes a step further, recommending screening for all men and women aged 65 to 75 with any history of tobacco use, and for men 55 or older who have a family history of AAA.
For women who have never smoked and have no family history, routine screening is not recommended because the condition is significantly less common in this group.
How the Aorta Is Monitored
Ultrasound is the standard first-line tool for checking the abdominal aorta. It’s noninvasive, uses no radiation, and is highly specific, meaning it rarely flags a problem that isn’t there (specificity above 99%). Its sensitivity is more moderate, catching 57 to 70% of aneurysms depending on their location. CT scanning without contrast performs better at detection, with sensitivity in the 83 to 89% range, and can identify aneurysmal changes that ultrasound misses. CT is often used when more precise measurements are needed, particularly before planning any intervention.
For small aneurysms (under 5.5 cm), the standard approach is regular ultrasound surveillance rather than immediate treatment. Clinical trials comparing early surgical repair to watchful monitoring for aneurysms between 4.0 and 5.5 cm found no meaningful difference in six-year survival rates. Surgery is typically considered once the aneurysm reaches 5.5 cm, or if it’s growing rapidly (more than 0.7 cm in six months or more than 1 cm in a year). Aneurysms that cause symptoms at any size are also considered for repair.
Atherosclerosis in the Abdominal Aorta
Beyond aneurysms, the abdominal aorta is a common site for atherosclerosis. Plaque buildup along its walls can stiffen the artery, raise blood pressure, and reduce blood flow to downstream organs. When atherosclerosis narrows the renal arteries, the kidneys receive less blood and respond by triggering hormonal signals that push blood pressure even higher, creating a cycle that can damage both the kidneys and the cardiovascular system over time. The same process in the iliac arteries at the bottom of the aorta can reduce blood flow to the legs, causing pain with walking.
The risk factors overlap heavily with those for aneurysms: smoking, high blood pressure, high cholesterol, diabetes, and aging all accelerate plaque formation. The abdominal aorta is particularly vulnerable because of the turbulent blood flow at branching points, where arteries split off at angles that create mechanical stress on the vessel wall.