Introduction: The cemento-ossifying fibroma (COF) comprises a benign, solid tumor, which is rich in cells and fibrous stroma, and variable parts of mineralized tissue (bone/cementum) [1]. COFs typically occur among the second and fourth decade of life and are most commonly located in the region of the lower jaw. Females are affected more often than males [2,3]. COFs show radiopaque and radiolucent variations in radiographic images and can be asymptomatic for a long time [3]. To get a distinctive diagnosis, it is necessary to perform a histological evaluation. However, for rare tumor entities, dignity cannot be ascertained surely- neither clinically nor radiologically or in histological ways. Case description: A 24-year-old female was admitted to our center with the radiological finding of a solitary mass, which expanded up to 3x 2.4 cm in the right lower jaw, infiltrating parts of the lingual cortical bone with direct contact to the roots of the teeth 46 and 47. Clinically, no further abnormalities could be detected. After the initial tumor resection, the histological examination resulted in the diagnosis of a cemento-ossifying fibroma. Still, a low-grade osteosarcoma could not be ruled out. In the course of a radical tumor resection, a partial continuity resection of the lower jaw was performed and a patient-specific, microsurgical, musculo-osseous iliac crest transplant was harvested using CAD/CAM templates and inserted into the bony defect. The postoperative course was uneventful and the definite histological examination confirmed the diagnosis of a COF. Follow-ups showed no evidence of a recurrence. After implant loading and prosthetic rehabilitation, the patient is now free of complaints and very satisfied with the outcome of the therapy. Conclusion: Even after an excisional biopsy, in some cases the dignity of tumors of the lower jaw cannot be determined exactly. Therefore, extensive findings often require a radical surgical procedure with primary bone reconstruction, even if the tumor is being classified as benign lesion later on. COFs require an early radical surgical handling, because on the one hand cases with inoperable tumor size have been described and on the other hand COFs bear the potency to recur and can possibly even undergo malignant transformation. Against this background, the follow- up after tumor resection should amount to no less than ten years [4,5]. Keywords: cemento-ossifying fibroma of the lower jaw, benign tumor of the lower jaw, tumor resection, rare bone tumor lower jaw