OBJECTIVE: To evaluate the effectiveness of montelukast as add-on therapy for patients diagnosed with asthma and concurrent allergic rhinitis who remain uncontrolled while receiving inhaled corticosteroid (ICS) monotherapy or ICS/long-acting beta-2-agonist (LABA) therapy in a community practice setting.DESIGN: An eight-week, multicentre, open-label, observational study. Patients were 15 years of age or older and, while treated with an ICS or ICS/LABA, had allergic rhinitis and uncontrolled asthma symptoms by at least two criteria as per the Canadian Asthma Consensus Guidelines. The primary outcome measure was the percentage of patients with controlled asthma symptoms after eight weeks of treatment with montelukast 10 mg once daily added to ICS or ICS/LABA therapy.RESULTS: In total, 1004 patients participated in the survey phase of the study. Of these patients, 319 continued in the treatment phase and 301 (94.4%) completed the eight-week assessment. At baseline, all patients had uncontrolled asthma symptoms based on the Canadian Asthma Consensus Guidelines; at the eight-week assessment, 229 patients (76.1%) achieved asthma control. According to the Asthma Control Questionnaire (as determined by scores of 0.75 or less), 164 patients (54.7%) achieved well-controlled asthma at week 8. The mean (± SD) Asthma Control Questionnaire score decreased from 2.03±0.80 to 0.92±0.80 (P<0.001) for all patients, representing a clinically significant improvement. A statistically and clinically significant reduction in the overall Mini Rhinitis Quality of Life Questionnaire score was achieved with a decrease from 2.57±1.20 to 1.12±1.00 (–1.45±1.35; P<0.001). Patient and physician satisfaction rates with montelukast add-on therapy were also significantly increased when compared with baseline treatment.CONCLUSION: Montelukast add-on therapy is effective for managing asthma and allergic rhinitis symptoms in patients who were previously uncontrolled with ICS or ICS/LABA treatment.