Cemento-osseous dysplasia may present as a focal, periapical or florid lesion in the mandible or maxilla. The lesion may sometimes appear similar to peri-radicular lesions on a periapical radiograph. This report presents a case with irreversible pulpitis and root resorption as well as a mixed radiolucent/radiopaque lesion around a mandibular molar tooth root. Root canal treatment was performed and because of the radiographic signs of root resorption and the patient's fear of having a malignant disease, periapical surgery was also performed. The histopathology report confirmed the presence of florid cement-osseous dysplasia which was mimicking apical periodontitis. Follow-up radiography 12months after the surgery illustrated complete healing of the radiolucent area. © 2011 Australian Society of Endodontology.