Association of ectopic supernumerary tooth in the maxillary sinus with dentigerous cyst is quite uncommon. The cause is unknown in most of the cases but developmental disturbance, pathologic processes or iatrogenic factors have been implicated. Most are symptomless and usually take an insidious course. Those with symptoms will mimic rhinosinusitis. The ectopic tooth can be found incidentally on routine plain radiographs of the paranasal sinuses, skull or panoramic radiographs. We present the case of a patient of large dentigerous cyst associated with an ectopic supernumerary tooth in the right maxillary sinus.