Purpose: Leukotriene receptor antagonists are used in asthma and rhinitis treatment. Pharmacovigilance data have suggested an association between montelukast and depression, but the association has not been established in controlled study designs. We described the association between initiation of montelukast and depression, using prescriptions of antidepressants as a surrogate marker, and assessed whether the association was related to the underlying asthma disease. Methods: We performed a symmetry analysis, with a study period from January 1, 2000 to December 31, 2016, using 3 nationwide Danish registers. We included all adults, who filled their first prescription of montelukast and antidepressants within an interval of 1 year. In the absence of an association between montelukast and antidepressant use, a symmetrical distribution of prescriptions is expected before and after montelukast initiation (ie, a sequence ratio [rc] of 1.0). We subcategorized the subjects after the severity of underlying asthma disease. Results: In total, 4450 subjects filled their first prescriptions of both montelukast and antidepressants within a 1-year interval: 2434 redeemed their first prescription of montelukast before antidepressants, and 2016 redeemed the medications in the opposite order (rc 1.21 [95% CI 1.14-1.28]). We found rc above unity in groups with long-acting asthma treatment, but no increase in antidepressant prescription, when stratifying by the asthma severity. Conclusion: We found a weak association between the use of montelukast and the risk of being prescribed an antidepressant, unlikely to be of clinical relevance. Stratified analyses suggest that this association may relate to asthma, rather than to montelukast.