Ankylosing spondylitis (AS), the prototype of the spondyloarthritides (SpA), is a disease subset but also a possible outcome of the SpA. Early diagnosis of sacroiliitis, the most frequent clinical symptom often accompanied by inflammatory back pain, and other inflammatory lesions of the spine such as spondylitis and spondylodiscitis, can be visualized early by magnetic resonance imaging (MRI). Chronic changes such as syndesmophytes are well detected by conventional x-rays of the spine, mostly lateral, in the lumbar spine also a.p. Active spinal inflammation can be demonstrated by MRI by using either the fat saturating STIR technique or by application of the contrast agent gadolinium-DTPA. This is especially useful in early and active disease, in young women and in children, and for the differential diagnosis of septic sacroilitis. Because of the efficacy of the novel biologic agents directed against TNFalpha such as infliximab and etanercept in SpA there is a need for spinal imaging techniques that are more sensitive than conventional x-rays. The available scoring tools are limited in their sensitivity to change. Novel approaches using MRI have been recently proposed.