The term 'spondyloarthritides' (SpA) comprises ankylosing spondylitis (AS), reactive arthritis, arthritis/spondylitis with inflammatory bowel disease, and arthritis/spondylitis with psoriasis. The main links between these diseases are an association with HLA-B27 and a similar clinical picture. Patients normally present with chronic low back pain or asymmetrical arthritis, predominantly of the lower limbs, and an overlap of these symptoms often occurs. AS is regarded as the most severe subtype. Recent attention has focused on earlier diagnosis of AS among patients with chronic low back, and this is becoming more important as effective therapies for early treatment have become available. AS is a disease of young people, normally starting in the third decade of life. The incidence and prevalence rates of AS, and of SpA as a whole, are strongly dependent and are directly correlated to the prevalence of HLA-B27 in a given population. Incidence rates of 0.5-8.2/100 000 population and prevalence rates of 0.2-1.2% have been described for AS, and about double these figures have been reported for SpA.