Ankylosing spondylitis is a type of chronic arthritis that is most often diagnosed in adolescents and young adults. The disease usually develops in the spine, but it can also affect the knees, hips, shoulders, and other joints, as well as other parts of the body. The exact cause of ankylosing spondylitis is not yet known, but it is thought that a combination of environmental, genetic, and immune system factors may play a role in its development. Symptoms of the disease may begin with back pain and stiffness. Early in the disease, many people experience constant pain and stiffness; however, as the disease progresses, periods without pain and stiffness become more common. While severe cases of ankylosing spondylitis may require surgery, treatment for most people with the disease involves lifestyle changes, medication, and regular monitoring.