Background: We aim to assess the impact of montelukast on paediatric patients with asthma/allergic rhinitis, measured using patient-reported outcome measures, compared with other treatments or placebo. Methods: Protocol registration CRD42020216098 (www.crd.york.ac.uk/PROSPERO). MEDLINE and Embase databases were used to conduct the search. Two authors independently selected studies and extracted data, and a third reviewer resolved discrepancies. Meta-analyses were constructed to estimate the standardised mean difference (SMD) using a random-effects model. Results: Out of 3937 articles identified, 49 studies met the inclusion criteria, mostly randomised clinical trials (sample sizes: 21-689 patients). The SMD of change pooled estimators for t...