OBJECTIVES: Absenteeism is a major cause of indirect costs of illness. In Poland precise data regarding days of work lost due to illness are collected by Social Insurance Institution (ZUS). The aim of this study was to estimate absenteeism costs in Poland in 2007 based on average monthly gross wages and salaries. METHODS: Human capital approach was used to estimate absenteeism costs. We used ZUS and Central Statistical Office (GUS) data. Average monthly gross wages and salaries estimates were calculated taking into consideration sex and province specific data. The analysis was based on an assumption that number of missed days includes only working days (252 days per year). This assumption was tested within the range of 226 to 365 days (either including all calendar days or additionally subtracting 26 days of holidays). Values are presented in Euro (exchange rate: 1 Euro=4,50 PLN). RESULTS: Total costs of absenteeism in 2007 were estimated to amount of €5.3 billion (range €3.7-€5.9 billion). In Silesia province the cost of day of sickness absence estimated per person employed was nearly twice as high as in Podlaskie province. Total costs of absenteeism calculated based on GDP per capita were similar, however there were some differences among territory specific estimations. Cost data based on GDP per capita or average monthly gross wages were approximately twice as high as ZUS data on the amount of funds spent on sick pay. CONCLUSIONS: Given that several predictors of sickness absence are not accounted to GDP per capita or average monthly gross wages and salaries based estimation, it seems that ZUS data on amount of mean sick pay may provide a reliable tool for absenteeism costs estimation in Poland.