Background The paediatric population has a high incidence of sleep-related breathing disorders (SRBD). A notable risk factor is the presence of craniofacial abnormalities. The objective of the study was therefore to survey the prevalence of SRBD in patients presenting for interceptive treatment. Material and Methods Prospective study with a sample of 249 healthy patients. The “Paediatric Sleep Questionnaire” and “Sleep Disturbance Scale for Children” were completed by the children’s parents and the results were evaluated. All patients had their medical records reviewed and underwent orthodontic diagnosis by oral examination, as well as dental cast and cephalometric analysis. Finally, we compared the results of the pre- and post-treatment questionnaires of 50 patients in the sample. Results Based on the results of the questionnaires, 22.8% of the study sample had SRBD. No statistically significant correlation was found between SRBD and the anthropometric characteristics and occlusal variables assessed. According to the cast analysis, patients with SRBD had a smaller maxillary width ( p <0.003), and according to the cephalometric study, less overbite ( p <0.003). Furthermore, the prevalence of SRBD was higher among patients with a history of adenotonsillectomy ( p <0.02). Comparison of the results of pre- and post-treatment questionnaires revealed significant differences after orthodontic treatment ( p <0.0005). Conclusions It is necessary to identify the presence of SRBD in orthodontic patients given its high prevalence. Patients with SRBD have a smaller maxillary width and less overbite. Key words: Sleep-related breathing disorders, paediatric sleep questionnaire, cephalometry.