Endodontic treatment of teeth with perforating internal root resorption represents a clinical challenge. In most cases, extraction of the tooth and subsequent replacement with an osseointegrated implant is indicated. Presented herein is a case report of a maxillary lateral incisor with advanced perforating internal root resorption in the middle third of the root and the presence of a sinus tract. Mineral Trioxide Aggregate (MTA) was used with the aid of a surgical microscope in order to fill the resorption area after conventional root canal therapy of the apical segment. At the follow-up after 11 years and 8 months, the patient was clinically asymptomatic and the sinus tract had disappeared. The radiographic examination and computerized tomography indicated periodontal bone repair. (J Oral Sci 54, 127-131, 2012)