Although x-rays are still the standard for the assessment of structural sacroiliac joint changes and the diagnosis of ankylosing spondylitis (AS), magnetic resonance imaging (MRI) sequences are necessary for assessment of active sacroiliitis. Conventional radiographs of the spine are the basis for the detection of AS-related structural spinal changes, such as syndesmophytes and ankylosis. MRI of the spine is useful for the assessment of inflammatory changes, and potentially for the diagnosis of early and active stages of the disease. MRI sequences useful for the assessment of active disease are the short tau inversion recovery, the T2-fat saturated and the T1 post-gadolinium MRI sequences. For assessment of structural changes, the T1-weighted MRI sequence is used. Both sacroiliac joint and spinal changes can be quantified by evaluated scoring systems. These systems are mostly used in clinical trials to quantify the impact of therapy, such as anti-tumor necrosis factor-α agents, on spinal inflammation.