INTRODUCTION: Patients who have malocclusions caused by bone diseases come to see the dentist for the orthodontic treatment. One of these diseases is fibrous dysplasia. The aim of this study was to present the patient with the active form of fibrous dysplasia who reported to the Orthodontic Department of Pomeranian Medical University in Szczecin for treatment. MATERIAL AND METHODS: We used the patient's own documentation, photos, radiological view and histopathological investigations. RESULTS: The extraoral, clinical examination revealed the asymmetry of the face on the left side, while the intraoral examination showed the convex lesion similar to an egg on the palate which crosses the medial line and clear "distension" of the alveolar bone in the direction of the oral vestibule. The dysplastic lesions are extensive and cause numerous malocclusions and disorders of the symmetry. The radiological and histopathological examinations were added to the clinical examination. The panoramic radiographs have shown the asymmetry and heterogenic structure of the bone with areas of"ground glass". Computer tomography demonstrated bumpy thickening of the zygomatic bone, maxilla, and a great wing of the sphenoid bone and almost completely filled maxillary sinus. The histopathological examination is the confirmation of the diagnosis of fibrous dysplasia. It demonstrates immature bone. CONCLUSIONS: The diagnosis of fibrous dysplasia commands the periodic observation and the postponement of the orthodontic treatment in the stage of active development of lesions, but when the overgrowth impairs the function, there is the necessity to use surgical and radical excision to remove lesions. We must pay particular attention to the possibility of malignant transformation of these lesions.