Ankylosing spondylitis is a chronic rheumatic disease leading to functional limitations. This has an important impact on participation in the labour force, with high disease-related work disability. As for cost-of-illness studies, which estimate the costs related to a disease, the cost of lost productivity is the major contributor to the total costs of ankylosing spondylitis. Because of the low prevalence of the disease, the costs related to ankylosing spondylitis are a relatively small part of the costs of all diseases to society. However, given the early and the important long-term functional loss, the lifetime costs and socio-economic impact for the individual patient are likely to be high. Because poor physical function is the major determinant of high direct and productivity costs, new (biological) treatments with effects on long-term functional disability will potentially reduce the economic impact of the disease for society and patients.