OBJECTIVES. The authors report a case of supernumerary tooth (mesiodens) in a 10-year-old patient. The only clinical signs were a wide middle diastema and the rotation of an upper central incisor; the tooth was removed and the patient was controlled for a year. METHODS. Radiological imaging showed the contiguity of supernumerary tooth with the floor of nasal cavity. CT Dentascan was performed to assess mesiodens dimensions and its relationships with adjacent structures. The tooth was extracted under general anesthesia. CONCLUSIONS. Supernumerary teeth are not rare in everyday dental practice and they often represent a casual X-ray finding, as in the case reported in this study.