Background Rapid maxillary expansion (RME) is an orthodontic procedure used to correct transverse maxillary deficiency. Due to the anatomical relationship between the palate and the nasal cavity, RME promotes an increase in nasal dimensions, which should hypothetically improve nasal respiratory function. Objective: This review aimed to systematically verify studies that assessed the effects of RME on nasal patency in mouth-breathing children and adolescents. Material and Methods An electronic search was performed in the MEDLINE databases via OVID, Scopus and EMBASE. The terms were: “children and adolescents”, “rapid maxillary expansion” and “mouth breathing”. The search was conducted in October 2019, according to the criteria of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). The assessment of the quality of the studies was conducted by two evaluators, using the Fowkes & Fulton´s guidelines for critical appraisal of medical research. Results 475 titles were identified and 18 articles were selected. All of them showed high methodological quality, but without randomized clinical trials. The instruments evaluated were: teleradiography, frontal postero-anterior radiography, computed tomography, acoustic rhinometry and computed rhinomanometry. Conclusions This review shows that RME promotes the enlargement of dental arches and of the nasal and maxillary structures, with improved mouth breathing in the short term. However, its long-term benefits could not be proved so far. More robust results of the effectiveness of RME in mouth breathing can be achieved with meta-analysis studies, with a consensual definition of the long-term follow-up period after RME. Key words: Child, adolescent, maxillary expansion, palatal expansion, mouth breathing.