Pyomyositis is a rare complication of chemotherapy. A 35-year-old male patient with myelodysplastic syndrome developed Stenotrophomonas maltophilia bacteremia shortly after chemotherapy, and Stenotrophomonas maltophilia-related pyomyositis was encountered after recovery from neutropenia. He recovered completely after surgical drainage and a protracted course of antibiotic treatment. It is postulated that subclinical myopathy, immunosuppression secondary to the malignancy, or chemotherapeutic drugs may predispose to pyomyositis. Early recognition of this unusual complication in a cancer patient undergoing chemotherapy can prevent further catastrophes.