Introduction: Osteosarcoma is characterized by its rarity and malignant nature, leading to difficulty in diagnosis. Observation: We present the case of a young woman observed by her orthodontist for a recent asymptomatic intraoral mass. The first anatomo-pathological result of the sample was a benign lesion, but rapid recurrence of the lesion led to the samples being retested, resulting in the diagnosis of osteosarcoma. Discussion: The most common symptom associated with osteosarcoma is painless swelling, sometimes associated with dysesthesia and/or limited mouth opening. The radiological signs may be of the osteogenic- or osteolytic-type. After histological confirmation the treatment of this tumor requires surgical excision sometimes combined with chemotherapy. Conclusion: Osteosarcoma should be part of the differential diagnosis when a patient has an intraoral bone tumor.