BACKGROUND: Evidence is growing that an adverse psychosocial work environment increases sickness absence, but little is known on the magnitude of this problem or the impact of specific factors. METHODS: Psychological demands, decision authority, skill discretion, social support from colleagues or supervisor, predictability, and meaning of work were assessed with questionnaires at baseline and sickness absence was followed-up in employers' registers for 1,919 respondents (response rate 75.2%, 68% women, mainly low-skilled jobs) from 52 Danish workplaces during a 2-year period. Etiologic fractions (EFs) were calculated with the most favorable quartiles as reference. RESULTS: In the fully adjusted model, the following EFs were found: decision authority: 12%; social support from supervisors: 8%; psychological demands: 6%; and predictability: 5%. In total, the seven psychosocial factors explained 29% of all sick-leave days. CONCLUSIONS: The results suggest that improving the psychosocial work environment among the less favorable 75% may prevent substantial amounts of absence.