Supernumerarypremolars have been reported to occur in 0.29% of the general populationand to represent about 9.1% of all supernumerary teeth. Most of the supernumerary teeth reported in the literature were detected by radiographsas most of them were unerupted or impacted.Asearch of the literature revealed not many cases of fully erupted and well aligned supernumerary premolars being reported. A case of a unilateral transposed supernumery premolarthat had erupted into alignment is presented here. The remarkable featureof this case is that the supernumery premolar is transposed between the first and second permanent maxillary molars. The etiology of supernumeraryteeth is also reviewed.