The authors report an unusual case of myelodysplastic syndrome (MDS) associated with relapsing polychondritis (RP), which developed at almost the same time as MDS. The initial diagnosis was MDS, refractory anemia (RA) subtype, according to the FAB classification. Symptoms of RP were apparently controlled by oral administration of prednisolone (PSL), although MDS was not. Within 1 month after the diagnosis, monocytosis and thrombocytopenia without excess of blasts became prominent and transformation from RA to chronic myelomonocytic leukemia (CMML) was recognized. Combination chemotherapy including daunorubicin (DNR) and cytosine arabinoside (ara-c) did not subdue the progressive monocytosis and thrombocytopenia. Finally, the patient died of pulmonary hemorrhage 3 months after the onset of the disease. The prognosis of MDS may be poorly influenced by association with RP.