The most serious complication of an abdominal aortic aneurysm is rupture. When rupture occurs, more than half of people die before getting medical attention.

A second complication is the formation of a blood clot in the aorta. When an aneurysm develops, it may result in damage to the wall of the blood vessel. The damage leads to clot formation. A blood clot can narrow the diameter of the aorta, leading to a decrease in blood flow and a resulting lack of blood and oxygen (ischemia) to areas "downstream" from the clot. Additionally, pieces of the blood clot can break off and travel through the bloodstream (embolize) and lodge elsewhere in the bloodstream. This blocks blood flow and causes damage to tissue beyond the blood clot.

For instance, if a blood clot breaks off and travels to the iliac artery, which carries blood to the pelvis and legs, it can block blood supply to the foot or toes and cause a "cold foot" or another manifestation of acute vascular disease. This usually requires emergency surgery.

An inflammatory aneurysm can cause complications, such as fever, weight loss, and symptoms of a chronic disease. A massive inflammatory response may affect body parts close by, including part of the small intestine (duodenum), the ureter, or the veins to the kidney. Any of these structures can become obstructed by the inflammation.