Montelukast, a leukotriene receptor antagonist, was marketed in 1998 as an oral supplementary treatment to patients with mild to moderate asthma. The aim of this study was to describe the early discontinuation pattern among montelukast users in Denmark in the period of 1 March 1998 to 31 December 2016, and to identify demographic characteristics possibly associated with early discontinuation. This nationwide drug utilization study was based on data collected from three nationwide Danish registers. All montelukast users who redeemed at least one prescription in the study period were identified. Early discontinuation was defined as failing to fill a second prescription for montelukast within at least a year after the initial montelukast prescription. Among 135,271 included montelukast users, 47,480 (35%) discontinued the use of montelukast after a single redeemed prescription. The trend in early discontinuation increased throughout the years. The most predominant demographic risk factors for early discontinuation were prescription for only nasal topical anti-allergic treatment up to a year prior to montelukast initiation [adjusted odds ratio (OR) 2.25; 95% confidence interval (CI) 2.13-2.38], as well as suspected off-label use (adjusted OR 2.02; 95% CI 1.97-2.08). Several risk factors were associated with a decreased risk of early discontinuation; most pronounced was a prescription of inhaled corticosteroids within a year up to montelukast initiation [adjusted OR 0.47 (95% CI 0.46-0.49)]. Early discontinuation was more pronounced after patent expiry in 2012 [adjusted OR 1.42 (95% CI 1.38-1.45)]. In conclusion, we found that early montelukast discontinuation increased during the last 19 years. Appropriateness of the treatment indication as estimated by concomitant prescription of adequate inhalation therapy was associated with a low risk of early discontinuation. A more pronounced early discontinuation was observed after patent expiry in 2012, which could reflect a more liberal approach to montelukast prescription.