A psoas abscess is an abscess in one of the psoas muscles which extend from the lower spine into the groin. There are a number of potential reasons for one of these muscles to become abscessed, and it can sometimes be tricky to diagnose an abscess in the psoas muscle, as the symptoms are not necessarily obvious. Fortunately, the prognosis for patients with this problem is very good, especially when intervention is provided early.

A primary psoas abscess occurs when bacteria such as Staph bacteria get into the muscle, creating an area of inflammation and infection which often fills with fluid, including pus. This is most commonly seen in children, although it can appear in people of any age. A secondary abscess occurs when infection elsewhere in the body spreads to this muscle; historically, it was most commonly seen in patients with spinal tuberculosis, also known as Pott's Disease. Today, it is more commonly associated with infections of the bowels, kidneys, or spine.