Ankylosing spondylitis (AS) is the prototype of the spondyloarthritides (SpA). AS is a disease subset but also a possible outcome of SpA. Early diagnosis of sacroiliitis, the most frequent clinical symptom frequently 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). Spinal inflammation can be demonstrated by MRI using either the fat-saturating short tau inversion recovery (STIR) technique or by application of the contrast agent gadolinium-diethylenetriamine pentaacetic acid (DTPA). This is especially useful in early and active disease, in young women and in children, and for the differential diagnosis of septic sacroiliitis. Because of the efficacy of the novel biological agents directed against tumour necrosis factor-alpha (TNF-alpha) - such as infliximab and etanercept - in SpA there is a need for spinal imaging techniques more sensitive than conventional X-rays. The available scoring tools are reviewed and novel approaches using MRI are presented.