Burnout is a state of emotional exhaustion, feelings of reduced personal accomplishment, and withdrawal from work thought to occur as a consequence of prolonged occupational stress. The condition is not included in the diagnostic classifications, but is considered likely to develop into depressive disorder in some cases. We examined the prospective association between burnout and antidepressant treatment, as an indicator of clinically significant mental disorder. We further investigated potential effect-modifiers of the association, to identify factors that may prevent this progression of burnout. We used questionnaire data from a three-wave study of Danish human service workers conducted during 1999-2005, linked with national register data on purchases of antidepressants (ATC: N06A). We included 4788 observations from 2936 individuals (81% women) and analysed data by Aalens additive hazards modeling, examining the risk of entering antidepressant treatment in relation to the level of work-related burnout measured by the Copenhagen Burnout inventory. As effect-modifiers we examined both sociodemographic factors and a range of psychosocial work environment factors. The level of burnout predicted antidepressant treatment. This association was modified by sex (p < 0.01). In men, high vs. intermediate burnout was associated with a 5% increased risk of antidepressant treatment per year of follow-up. This risk difference was 1% for women. Due to the sex specific patterns, we restricted effect modification analyses to women. We found no effect-modification by the examined work environment factors, though a sensitivity analysis indicated a possible stronger association in women of lower occupational position. In conclusion, burnout predicted antidepressant treatment, with a stronger association in men than women. We found no evidence of effect-modification by any of the examined psychosocial work environment factors.