BACKGROUND Obstructive sleep apnoea (OSA) syndrome represents a significant medical problem due to numerous consequences that may follow it. OBJECTIVE The aim of the study was to analyze morphology of the maxilla in children with mouth breathing, and to assess possible characteristics in persons with marked clinical features of OSA. METHODS The sample comprised of 60 examinees aged from 8-10 years, all mouth-breathers. The following X-ray cephalometric parameters were measured: angle of maxillary pragmatism, cranial base angle, angle between the palatal plane and the anterior cranial base, maxillary length, distance from the most prominent labial surface of the maxillary central incisor to NA line, angle between the axis of the upper maxillary incisor and NA line. Following parameters were obtained from the casts: anterior and posterior width of the maxillary arch, height of the maxillary arch, index of the palatal height, as well as the apical base length. Assessed values were then compared to the corresponding norms. RESULTS Compared to the corresponding norms, statistically significant lower values were determined for the following parameters of the sample: SpP/SN, AW, PW, AB. CONCLUSIONS Analysis of the morphological characteristics of the maxilla in mouth breathing children showed characteristics also present in persons with marked clinical features of OSA syndrome, such as a narrow maxilla, insufficient apical base length, as well as the reduced angle of the palatal plane angle to the anterior cranial base. All these suggest a possible increased risk of developing OSA syndrome in children's later age.