Ankylosing spondylitis is a chronic inflammatory joint disease that predominantly affects the sacroiliac joints and spine. Its pathophysiology remains one of the most vexing enigmas of rheumatology. However, new insights have been provided by the recent identification of susceptibility genes other than HLA-B27; evidence of a pivotal role for several proinflammatory cytokines including interleukins 23 and 17; and the recognition that inflammation and structural progression proceed separately from each other.