OBJECTIVE: To determine the work-relatedness of mood disorders. METHODS: From 2001–2005, we followed up all economically active people in Denmark, aged 20–59 years as of January 2001, for hospital contact due to mood disorders. We calculated gender-stratified standardized incidence ratios (SIR) by industry. Using the distribution of the SIR values as input, we used a Monte Carlo simulation to estimate what proportion of the mood disorder cases could be regarded as work-related and denoted them as excess fractions. RESULTS: In total, we observed 10 731 cases of mood disorder among the women and 8305 among the men. There were four industries among women and 13 among men that showed elevated SIR with confidence intervals not including unity. The excess fractions without social group adjustment were 0.248 [95% confidence interval (95% CI) 0.173–0.325] for the women and 0.363 (95% CI 0.294–0.433) for the men. The respective fractions with adjustment for social group were 0.233 (95% CI 0.162–0.303) and 0.361 (95% CI 0.293–0.430). CONCLUSION: A substantial proportion of mood disorders among working people can be regarded as work-related. Hence, the workplace is an interesting arena for primary interventions.