Histiocytic sarcoma, a rare hematopoietic neoplasm with evidence of histiocytic differentiation, is often refractory to conventional chemotherapy and radiotherapy, and its prognosis is generally dismal. The optimal management of this malignancy has not been established. We report a case of 8-year-old girl with histiocytic sarcoma involving the left femur. The tumor rapidly responded to a combination of cladribine and high-dose cytosine arabinoside, an aggressive salvage regimen for refractory Langerhans cell histiocytosis, and became impalpable during the first cycle. The patient has remained in complete remission more than 7 years from diagnosis.