To salvage an uneruputed tooth within a dentigerous cyst, the retransplantation of the unerupted premolar involved in the dentigerous cyst was performed. In the present case a dentigerous cyst with the impacted maxillary second premolar of a 10-year-old boy was removed, because of the missing eruption after marsupialisation of the premolar 4 months earlier. Covering the crown and the one third of root, the cyst was removed from the tooth, and the premolar was retransplanted into a cavity created between the premolar and first molar in the maxilla. The tooth was fixed with resin and a twisted wire for 1 month. Two years after transplantation, the tooth responded positively to pulp vitality tests but did not move toward the occlusal line, and dental X-ray showed a lamina dura, mineralisation of the pulp cavity, no root resorption and development.