We present the case of a 32-year-old man with a diagnosis of type-III osteogenesis imperfecta who developed a telangiectatic osteosarcoma in the proximal right tibia. An above-knee amputation was performed and after one-year follow-up, pulmonary metastatic lesions were detected on the thoracic CT scan. Palliative chemotherapy was proposed and to date the patient is still living and is under medical treatment. The association between osteogenesis imperfecta and osteosarcoma is rare. There are only ten confirmed reports of this unusual situation, but to our knowledge this is the first case reported with a telangiectatic osteosarcoma arising in this particular setting.