ASAS (ASsessment of Ankylosing Spondylitis) working group was founded in 1995 in Maastricht. The idea for ASAS came from Sjef van der Linden, professor of Rheumatology at University Hospital Maastricht, with a special interest in the field of ankylosing spondylitis. Désirée van der Heijde joined as a member of staff in Maastricht in 1994 starting a research line on outcome assessment in AS. From the beginning it was the idea to also develop a core outcome set (COS) for AS similar to what had been done for RA by Outcome MEasures in Rheumatoid Arthritis Clinical Trials (OMERACT), funded by Maarten Boer, also working at the same department. Therefore, ASAS was built after OMERACT with the aim to develop a COS for AS. The core set of domains and the subsequent selection of instruments was developed by ASAS and later endorsed by OMERACT. Members of the first steering committee were in addition to Sjef van der Linden and Désirée van der Heijde, Maxime Dougados (Paris, France), Asim Khan (Cleveland, US), Andrei Calin (Bath, UK) and Nick Bellamy (London, Canada).

The first step for the COS was collecting all measurements from the literature that had been used in AS. To discuss the results and make a selection of the various domains and instruments additional experts in AS were invited. This ‘working group’ met at the time of the EULAR Congress in Amsterdam in 1995. This was the first official ASAS meeting with the members of the working group, the first ASAS members.

The first ASAS meetings were always linked to EULAR, ACR and later the international SpA congress in Ghent. When TNFi became available for the treatment of AS, a meeting involving all ASAS members was organized in Berlin by Jürgen Braun and Joachim Sieper in 2003. The first consensus statement on the use of TNFi in AS was published as a result of the meeting. This marked the first annual ASAS meeting (usually called workshop), independently of the large rheumatology congresses and also to the broadening in the mission of ASAS.

The first bylaws were published in 2008. This was the time of the change of the meaning of the abbreviation. Since then, ASAS stands for Assessment in SpondyloArthritis international Society. The changes indicate that it was no longer a ‘working group’ but a more official status of society with international members. Ankylosing Spondylitis was changed in analogy to the broader concept of Spondyloarthritis, both axial and peripheral. Moreover, the focus of the society was much broader, including all aspects of SpA from diagnosis to assessment, from therapy to outcome of patients. There was also more emphasis on education.

The bylaws were updated in 2024. This was an important step in the professionalisation of the society. The bylaws defined the composition and roles of the Executive Committee (EC) and the Advisory Committee (AC), as well as rules for elections and duration of membership of these bodies. Also, the membership levels (full member, associate member and corporate member) were outlined. From 2013 the EC was expanded from six to nine members, and up to two non-voting advisors. From 2017 Young ASAS was installed.