Spondyloarthritis (SpA) represents a group of interrelated diseases with common clinical features and a close association with HLA-B27. Figures on the incidence and prevalence of diseases vary highly dependent on methodological differences between studies, the case definition used to classify disease and on the prevalence of HLA-B27 in the population studied. When summarizing the available literature, incidence rates of SpA are mainly based on the ESSG criteria and range between 0.48 and 63/100.000 while prevalence rates vary between 0.01 and 2.5%. For ankylosing spondylitis (AS), the most widely recognized representative of the SpA group of diseases, incidence rates of 0.44-7.3/100.000 and prevalence rates of 0.007-1.7% have been described in studies that were based on the (modified) New York criteria to classify cases. The incidence of psoriatic arthritis (PsA) varied from 3.6 up to 23.1/100.000 in different studies and prevalence between