Ectopic tooth eruption can occur in a wide variety of sites, including the mandibular condyle, coronoid process, palate, nasal cavity and maxillary sinus. An ectopic tooth may be permanent, deciduous or supemumerary. A case is presented in which an ectopic tooth was found in the left maxillary sinus of a 27-year-old male. Etiological factors leading to the emption or displacement of teeth are briefly reviewed and discussed.