Osteosarcoma most frequently affects long bones, particularly around the knee, and is therefore rare in the forearm. We report the case of a 67-year-old woman presenting with progressive lesion of the distal radius. A pathological diagnosis of osteoblastic osteosarcoma was suspected and was confirmed by needle biopsy. There had been two other cases of osteosarcoma in the same family. The patient was treated with neoadjuvant chemotherapy followed by amputation of the arm below the elbow.