In the past decade, major progress has been made in the recognition, classification and treatment of spondyloarthritis (SpA). Classification criteria have been developed for axial and peripheral SpA by the Assessment of SpondyloArthritis international Society (ASAS) as a response to new insight into the clinical picture and unmet needs. The ASAS criteria have contributed to a better understanding of the full spectrum of axial and peripheral SpA and of the potential for treatment. However, whether all patients fulfilling these criteria should be considered as having true SpA is a matter of debate. Furthermore, the implementation of the ASAS criteria might lead to an increase in the reported prevalence of SpA, as patients who were previously unidentified could now be classified as having the disease, which might have consequences for healthcare budgets. In this Review, the changes in the clinical picture and epidemiology of SpA are discussed in light of the ASAS classification criteria for SpA.