Objective: To identify individual and work-related predictors of long-term (8 weeks) sickness absence with psychiatric diagnoses (LSP). Methods: Data from the Oslo Health Study (response rate 46%) were linked to public registers. A total of 8333 subjects were followed from 2001 through 2005. Cox regression was used to compute hazard ratios for LSP. Results: At least one LSP was present in 7.8% of women and 3.9% of men. Poor support from superior had an independent and moderate effect. Path and linear regression analyses indicated that the effect of support from superior was mediated through mental distress and not the other way around. Selfreported mental distress had a strong independent effect. Conclusions: Women had a higher risk of LSP than men. Low education and poor support from superior and mental distress were found to be determinants of LSP.