OBJECTIVES: The study tested the hypothesis that a one-item workability measure represented an assessment of the fit between resources (the individuals' physical and mental health and functioning) and workplace demands and that this resource/demand fit was a mediator in the prediction of sickness absence. We also estimated the relative importance of health and work environment for workability and sickness absence. METHODS: Baseline data were collected within a Danish work and health survey (3,214 men and 3,529 women) and followed up in a register of sickness absence. Probit regression analysis with workability as mediator was performed for a binary outcome of sickness absence. The predictors in the analysis were as follows: age, social class, physical health, mental health, number of diagnoses, ergonomic exposures, occupational noise, exposure to risks, social support from supervisor, job control and quantitative demands. RESULTS: High age, poor health and ergonomic exposures were associated with low workability and mediated by workability to sickness absence for both genders. Low social class and low quantitative demands were associated with low workability and mediated to sickness absence among men. The mediated part was from 11 to 63 % of the total effect for the significant predictors. CONCLUSION: Workability mediated health, age, social class and ergonomic exposures in the prediction of sickness absence. The health predictors had the highest association with both workability and sickness absence; physical work environment was higher associated with the outcomes than psychosocial work environment. However, the explanatory value of the predictors for the variance in the model was low.