Histiocytic sarcoma is a rare, lymphohematopoietic malignant tumor comprised of tumor cells with the morphological and immunophenotypic features of mature histiocytes. A 35-year-old man presented with a disseminated histiocytic sarcoma that first occurred in the spinal cord and metastasized to the skin and lymph nodes. The tumor cells of the primary histiocytic sarcoma of the spinal cord were very large epithelioid cells with abundant eosinophilic cytoplasms and large, round-to-oval nuclei. In contrast, the metastatic histiocytic sarcoma of the skin was composed of relatively small polygonal cells with well-defined cell borders and high N/C (nucleus/cytoplasm) ratios. Immunohistochemically, both tumors were diffusely positive for histiocyte-associated antigens; but negative for epithelial, melanocyte, lymphoid, and dendritic cell antigens. It is important to recognize the morphological features and immunohistochemical characteristics of metastatic cells in order to ensure accurate diagnoses. (Korean J Dermatol 2016;54(3):199~202)