Objective: To examine whether low leadership quality predicts long-term sickness absence (LTSA) in Denmark. Methods: Using Cox models, we estimated the association between exposure to low leadership quality and onset of register based LTSA (more than or equal to 6 weeks) during 12-months follow-up among 53,157 employees without previous LTSA. Results: During 51,155 person-years, we identified 2270 cases of LTSA. Low leadership quality predicted LTSA with a dose-response pattern after adjustment for confounders. The hazard ratio (HR) of LTSA in the lowest compared with the highest quartile of leadership quality was 1.61 (95% CI: 1.43 to 1.82). Further, change from high to low leadership quality over time predicted risk of LTSA (HR = 1.42, 95% CI: 1.02 to 1.97) compared with persistent high leadership quality. Conclusions: Exposure to low leadership quality is a risk factor of LTSA in the Danish workforce.