The case of a male patient of 40 was first diagnosed histologically as fibrous dysplasia of the left mandible at our clinic on July 8, 1988. However, because there were the swelling and the bone absorption in the mandible in progress 2 months later, a biopsy was taken and his case was diagnosed as osteosarcoma. After intra-arterial chemotherapy from the superficial temporal artery with adriamycin, he received hemimandiblectomy with suprahyoidal neck dissection, which was followed by intravenous administration of a highdose of methotrexate and cisplatin about one month later. Unfortunately, the patient died of multiple metastases in thoraxes, lungs, heart, diaphragma, pancreas, etc. 13 months after the operation.
Some possible causes for this unsuccessful treatment to be taken up here are:
1. Prophylactic procedures to prevent metastasis of tumor cells were not taken at the first biopsy.
2. Insufficient information and clinical findings were given to the pathologist, which led to the wrong diagnosis at first.
3. It was 2 months after the first biopsy that the final diagnossin was established.
4. Postoperative chemotherapy started too late, and his medications were insufficient.