Histiocytic sarcoma is a rare hematopoietic malignancy with a poor prognosis. We report a 31-year-old woman who developed histiocytic sarcoma in the lower extremity. An open biopsy was required because a definitive diagnosis could not be made on the basis of a core-needle biopsy specimen. The diagnosis of histiocytic sarcoma was established using immunohistochemistry. No metastatic lesion was detected by PET-CT, and wide resection based on the procedure for a malignant soft tissue tumor was performed without neo-adjuvant chemotherapy. However, adjuvant radiotherapy was performed because there are few reports of histiocytic sarcoma being treated using surgery alone. During 35 months of follow-up, neither local recurrence nor distant metastasis has been observed. Our experience suggests that if a solitary lesion of histiocytic sarcoma can be resected with a sufficient margin, chemotherapy may be unnecessary.