This case report discusses the successful endodontic treatment of an open apex maxillary right permanent central incisor that had been avulsed and incorrectly replanted in a 7-year-old patient. The tooth was carefully re-extracted followed by cleaning of the alveolar socket and immediate replantation. However, pulp necrosis was diagnosed, and regenerative endodontic treatment was performed. The root canal system was disinfected by passive ultrasonic irrigation with 2.5% sodium hypochlorite. At the first visit, the tooth was repositioned and immobilized with an appropriate semirigid splint. After 14 days, the splint was removed, and the diagnosis of pulp necrosis was confirmed by thermal testing. The root canal was emptied, disinfected, and filled with calcium hydroxide paste, which was left in place for 7 days. At the third visit, calcium hydroxide was removed with hand files and passive ultrasonic irrigation, and the canal was filled with a mixture of double antibiotic paste (metronidazole/ciprofloxacin) and zinc oxide. The antibiotic paste was left in place for 30 days. At the final visit, the paste was removed and the periapical area stimulated with a #80 K-file to encourage clot formation within the pulp cavity. A mineral trioxide aggregate paste cervical plug was placed, and the tooth was restored with glass ionomer cement. Clinical and imaging (radiographic and tomographic) follow-up at 3, 6, 12, and 36 months showed endodontic success with continued root formation.