Bronchial asthma is an inflammatory disease, therefore the anti‑inflammatory agents are crucial in its management. Antileukotriene modifiers reveal such activity. They are recommended by GINA experts for usage in the monotherapy alternatively to low doses of inhaled glucocorticosteroids (ICS) on the 2nd step of asthma treatment or as the add‑on therapy to ICS on higher levels. The goal of this study was the evaluation of montelukast efficacy in outpatients aged 15 years and over suffering from persistent asthma in Poland. 11 250 patients were included to the observational program. The main inclusion criterion was previously treatment with montelukast no longer then one month. The physicians’ decision on the beginning of montelukast therapy had to be made independently of the patients’ participation in the study. The data was collected using uniform self‑prepared questionnaires during two routine visits in outpatient clinic performed in 8 week interval. The mean age of subjects was 36.79±15.62 years (range from 15 to 90). More than a half of participants (52.09%) were women. The asthma duration was usually between 2 and 5 years. Eighty three percent of subjects had atopic asthma. The main reason for beginning of montelukast therapy was insufficient asthma control (58.74%), the next was exercise induced symptoms (47.99%), in 40.85% of cases physicians indicated on allergic rhinitis coexistence. Montelukast was recommended as monotherapy in 11.35% of cases, and in 87.6% as add‑on therapy to ICS. During 8 weeks of observation the number of patients with currently completely controlled asthma increased form 8.22% (695) at visit 1 up to 44.48% (3808), the number of patients with partly controlled asthma decreased form 60.33% (5104) to 46.77% (4004), and the number of patients with uncontrolled asthma markedly decreased form 31.45% (2661) to 8.75% (749). In patients’ opinion the their overall health status markedly improved and the symptoms decreased. This observational study conducted in large group of asthmatics confirmed very good effectiveness of montelukast in achieving asthma control both in monotherapy and as add‑on therapy to the previous treatment.