This report presents a case of a patient who developed a supernumerary mandibular premolar during the course of orthodontic treatment. Evidence of this tooth comes from consecutive panoramic radiographs. It is not routine practice to screen for developing supernumerary teeth during orthodontic treatment. Therefore, the possibility of supernumerary tooth interference with occlusal development or orthodontic treatment should always be kept in mind. A brief review of literature concerning the late formation of supernumerary teeth is included. World J Orthod 2010;11:e94–e98.

Key words: supernumerary, mandibular, premolar, late-forming, orthodontic treatment