The aim of this case report was to present a treatment for severe inflammatory external root resorption. The condition developed due to the patient's neglect to seek adequate treatment following replantation of an avulsed maxillary left central incisor. Following diagnosis, treatment consisted of conventional endodontic therapy with calcium hydroxide dressings and definitive filling of the root canal after the resorption was controlled radiographically. A 24-month follow-up showed that the resorption process had stabilized and the patient was free of symptoms. Successful tooth replantation requires following the indicated therapy effectively. Nevertheless, when an inflammatory external root resorption occurs, adequate endodontic treatment to remove the necrotic content and bacteria is required, as is the use of calcium hydroxide dressings.