OBJECTIVES: The aim of this study was to assess the indirect costs caused by absenteeism associated with ankylosing spondylitis (AS) from the perspective of the Social Insurance Institution (ZUS) in Poland. METHODS: The estimates were based on data provided by ZUS referring to year 2012 and concerning absence from work due to the illness (sick leave), the amount of short term disability, the sufferers of which claim rehabilitation benefit, and the amount of permanent (or long term) disability, the sufferers of which claim disability pension. Costs were calculated with Human Capital Approach methodology taking into account Gross Domestic Product (GDP) per capita equaled 41 398PLN and Gross Value Added (GVA) per worker equaled 99 697PLN and were presented in 2012 prices in Polish zloty (PLN). RESULTS: Total indirect costs of AS in the year 2012 calculated using GDP per capita and GVA per worker in Poland were 21 299 578PLN and 51 294 959PLN, respectively. The highest component of indirect costs of AS was sick leave (56%). Long and short term disability costs constitute 6% and 39% of total indirect costs of AS, respectively. In 2012 Poland’s Social Insurance Institution database reported 3 500 patients on sick leave, 72 patients with short term disability and 7 patients with long term disability. Indirect costs per patient associated with sick leave were 3 400PLN and 8 188PLN calculated using GDP per capita and GVA per worker, respectively. Indirect costs per patient associated with short term disability were 16 602PLN and 39 983PLN respectively and associated with long term disability were as high as 1 171 958PLN and 2 822 381PLN, respectively. CONCLUSIONS: AS in Poland generated high indirect costs. The main component was sick leave; rehabilitation benefit and disability pension generated lower costs of lost productivity.