The aim of this paper is to report the diagnosis and successful clinical treatment of a maxillary central incisor with internal tunnelling replacement resorption. A case is presented in which internal replacement resorption in a maxillary central incisor developed after the patient had a bicycle accident 15 years previously. A preoperative radiograph showed two distinct radiolucent lesions in the apical middle of the root canal; one was irregularly oval shaped and the other, attached to the former, was horseshoe shaped. A computed tomography scan showed no evidence of periodontal ligament communication. Root canal treatment was completed in one visit and a 12-month follow-up showed no signs of periapical pathology. Keywords: computed tomography, internal replacement resorption, root canal, surgical operating microscope, tunnelling resorption