Back pain is common with up to 9% of the population consulting their GP with this problem each year. As the vast majority of these patients have non-specific back pain, it is often difficult to identify those with inflammatory disease such as ankylosing spondylitis (AS). It is critical to make this distinction as AS, if untreated, may cause significant morbidity with a substantial socio-economic impact both on the individual and society. Early diagnosis is particularly important as newer therapies are able to contain this condition and even induce remission in some cases. AS affects about 0.2-0.5% of the population. It is at least twice as common in men than women and most often manifests in the third to fifth decades. It is estimated that up to 5% of patients with chronic lower back pain in primary care have inflammatory disease. Diagnosis is usually delayed at least partly through lack of awareness of this condition. [With external links to the evidence base]