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Objectives: To identify differences in risk of sickness absence between socioeconomic groups, and to examine to what extent these differences can be explained by health behaviour and work environment factors. Design, setting and participants: A cohort of 5221 employees in Denmark interviewed in 2000 regarding health behaviours and work environment were followed for 18 months in order to assess their rate of sickness absence exceeding eight consecutive weeks. Based on employment grade, job title and education respondents were classified into five socioeconomic position (SEP) groups. Executive managers and academics were the reference group. Results: For both genders a social gradient in long-term sickness absence rates was evident. In men, controllin