At the age of 28, a 33-year-old male was diagnosed with malignant fibrous histiocytoma (MFH) with a primary lesion in the right maxillary sinus. Although arterial infusion chemotherapy (pirarubicin hydrochloride and carboplatin) was given, no tumor shrinkage was observed, and surgery was therefore performed to remove the tumor. Thereafter, the patient received autologous peripheral blood stem cell transplantation with high-dose chemotherapy (combination of ifosphamide, carboplatin and etoposide) as pretreatment. An increase in the peripheral leukocyte count was noted 56 months after the diagnosis of MFH was made. Cytogenetic study showed translocation (9;22)(q34;q11). Chronic myelocytic leukemia (CML) was therefore diagnosed. MFH was in a state of complete remission. The clinical course of this patient strongly suggests that this was a case of treatment-related CML that developed after chemotherapy for MFH. Treatment-related malignant blood diseases are known to include acute myelocytic leukemia and myelodysplastic syndrome, but reports of treatment-related CML are rare, although there have been some cases of treatment-related CML occurring several years after pretreatment.