Background: The paediatric population has a high incidence of sleepdisordered breathing (SDB). One notable risk factor for SDB is the presence of craniofacial abnormalities. The aim of this study was to evaluate the prevalence of SDB by means of questionnaires in patients who received interceptive treatment, to determine whether there is a relationship between the nature and duration of treatment and the prevalence of SDB, and to correlate cephalometric changes with the type of orthopaedic treatment received and questionnaire results. Materials and Methods: Prospective study of 203 patients who required interceptive treatment. Two sleep questionnaires (the Paediatric Sleep Questionnaire (PSQ) and the Sleep Disturbance Scale for Children (SDSC)) were used which were completed by the parents at baseline (T1) and after completion of interceptive treatment (T2). The results of the questionnaires were analysed, grouped according to the type of treatment received and related to 12 cephalometric variables on cephalometric radiography at T1 and T2. Results: The prevalence of SDB at T1 was 21.2% according to PSQ and 33% according to SDSC. The mean age at T1 was 8.5 years and the mean duration of treatment was 13.8 months. Between 10.8% (PSQ) and 17.2% (SDSC) of patients showed improvement in SDB after interceptive treatment (p<0.05). Treatment led to statistically significant cephalometric changes in the variables of mandibular length, maxillary length and overbite, with no significant differences between treatment groups or in relation to questionnaire results. Conclusion: Interceptive treatment achieves significant improvements in SDB. The type and duration of treatment do not affect the prevalence of SDB, although RPE is associated with a higher rate of improvement. The improvement in SDB is independent from the type of treatment and the cephalometric changes effected.