Regenerative endodontic treatment (RET) has been suggested for the treatment of traumatized necrotic immature teeth. There are only a few reports of using RET to treat a horizontal root fracture. The aim of this paper is to describe successful regenerative retreatment in a tooth with a horizontal root fracture and dens invaginatus. A 9-year-old boy presented with a horizontal root fracture in a central incisor. Pulp necrosis and inflammatory root resorption were observed. The tooth was treated by RET, including calcium hydroxide dressing between visits. After bleeding was allowed into the canal space, a collagen plug was placed as a barrier, and covered by a bioceramic material. At the completion of treatment, the resolution of the radiolucent lesion was evident. During follow-up, the tooth exhibited recurrent pathology at the fracture line. The patient was scheduled for retreatment of the tooth. Repeated RET included additional ultrasonic irrigation and calcium hydroxide dressing. One year after the completion of retreatment, the periradicular lesion resolved with continued maturogenesis of the apical fragment and approximation of the coronal and apical fragments that were attached by a calcified tissue and surrounded by the continuous periodontal ligament. Conclusion: This rare case report of retreatment after failed RET is notable for the repeated use of a regenerative procedure subsequent to a recurrent traumatic injury to the tooth. The repeated regenerative endodontic procedure (REP) resulted in the resolution of the periapical lesion and the reunion of the apical and coronal fragments. Clinical significance: Failure of an already successful RET due to a recurrent traumatic injury may be successfully treated by repeating the RET, particularly when the alternative treatment option is extraction.