Objectives: This study aims to compare the cephalometric radiographs of nasal or mouth-breathing children to determine the effect of mouth-breathing on craniofacial development. Patients and Methods: The study included 132 pediatric patients (65 males, 67 females; mean age 12.1 years; range, 10 to 14 years) having orthodontic treatment for malocclusion. Mode of breathing was assessed by an otorhinolaryngologist with the family history, physical examination, anterior rhinoscopy, and flexible nasopharyngoscopy. As a result of this examination, patients were classified as nasal-breathing patients (n=60) or mouth-breathing patients (n=72). Patients’ cephalometric radiographs, which were obtained for their orthodontic diagnosis and treatment, were used for the analyses. Results: Compared to nasal-breathing patients, mouth- breathing patients had retrognathic mandible, increased mandibular plane angle, and occlusal plane angle (p<0.05). Compared to nasal-breathing patients, mouth-breathing patients’ hyoid bones were located more superiorly and nasopharyngeal air spaces were narrower (p<0.05). Conclusion: We observed superiorly located hyoid bone, retrognatic mandible, and increased vertical face height in mouth-breathing children during the active growing period. Early diagnosis may be established with a multidisciplinary approach in mouth-breathing children, thus preventing the development of craniofacial and dental anomalies.