In 2003, several manuscripts on the classification of patients as having ankylosing spondylitis and the further development of outcome assessment tools have been published. It is obvious that the use of radiographic sacroiliitis is a problematic part of the classification criteria because there is major interobserver variation and is one of the causes of a long delay between onset of symptoms and diagnosis. Especially in patients without human leukocyte antigen B27, the diagnostic delay is long. Existing outcome tools, such as the Bath Ankylosing Spondylitis Disease Activity Index, have been adapted and validated for use in other languages. New instruments to assess quality of life (Ankylosing Spondylitis Quality of Life Index; Patient Generated Index) and physical functioning (World Health Organization Disability Assessment Schedule II) have been developed and validated for the use in ankylosing spondylitis. In addition, a new and feasible tool to assess enthesitis has been constructed and validated. Because fatigue is an important symptom for patients with ankylosing spondylitis, a recommendation to use a specific fatigue instrument was created. The statistically derived Assessment in Ankylosing Spondylitis response criteria have been compared with expert opinion and are strict criteria. Responders as defined by the Assessment in Ankylosing Spondylitis response criteria also are considered by the experts as responders.