Ankylosing spondylitis (AS) is the major subtype and a major outcome of an interrelated group of rheumatic diseases now named as spondyloarthritides (SpA). The most important clinical features of this group are inflammatory back pain (IBP), asymmetric peripheral oligoarthritis, predominantly of the lower limbs, enthesitis and specific organ involvement such as anterior uveitis, psoriasis and chronic inflammatory bowel disease. Aortic root involvement and conduction abnormalities are rare complications ofAS. For clinical purposes, five subgroups are differentiated: AS, psoriatic SpA (PsSpA), reactive SpA (ReSpA), SpA associated with inflammatory bowel disease (SpAIBD) and undifferentiated SpA (uSpA). The SpA are genetically linked, the strongest known contributing factor is the MHC class I molecule HLA B27, ARTS-7, and IL-23R, others still remain to be identified. Most frequently and characteristically, AS starts in the sacroiliac joints at a mean age of26 years affecting men only slightly more frequent than women. In about 80% of the patients the disease spreads to the spine where all three segments are affected, most frequently the thoracic spine. Osteodestructive structural changes such as erosions occur less frequently than osteoproliferative changes which are pathognomonic for AS being clinically impressive by their appearance as syndesmophytes and ankylosis. Established classification criteria for AS and SpA perform less well in early disease stages. This partly contributes to the delay of diagnosis which is in the range of 5-10 years-mainly due the high frequency of back pain in the population. Major factors to improve the rate of AS patients diagnosed early are HLA B27 and imaging of the sacroiliac joints. International recommendations for the management ofAS have been published. The conventional treatment is mainly based on NSAIDs, patients with peripheral arthritis may be treated with sulfasalazine and patients with persistently active disease benefit from therapy with anti-TNF agents. Physiotherapy is of major importance in the general approach to patients with AS.