Dentigerous cysts develop from unerupted and impacted permanent teeth. Very rarely, supernumerary teeth are associated with dentigerous cysts and constitute about 5-6% of all dentigerous cysts. Although these cysts are not common in the first decade of life, regular thorough inspection of radiographs is of importance, as indicated by this case report. This case shows how an impacted supernumerary canine developed a dentigerous cyst, engulfing the whole of the maxillary antrum.