INTRODUCTION: Mouth breathing (MB) is an etiological factor for sleep-disordered breathing (SDB) during childhood. The habit of breathing through the mouth may be perpetuated even after airway clearance. Both habit and obstruction may cause facial muscle imbalance and craniofacial changes. OBJECTIVE: The aim of this paper is to propose and test guidelines for clinical recognition of MB and some predisposing factors for SDB in children. METHODS: Semi-structured interviews were conducted with 110 orthodontists regarding their procedures for clinical evaluation of MB and their knowledge about SDB during childhood. Thereafter, based on their answers, guidelines were developed and tested in 687 children aged between 6 and 12 years old and attending elementary schools. RESULTS: There was no standardization for clinical recognition of MB among orthodontists. The most common procedures performed were inefficient to recognize differences between MB by habit or obstruction. CONCLUSIONS: The guidelines proposed herein facilitate clinical recognition of MB, help clinicians to differentiate between habit and obstruction, suggest the most appropriate treatment for each case, and avoid maintenance of mouth breathing patterns during adulthood.