Histiocytic sarcoma is a neoplasm arising from the histiocytes. Histiocytic neoplasms are among the rarest malignancies of lymphatic tissues. Occurs in less than 1% of all malignancies affecting lymph nodes and soft tissues [1,2]. The exact incidence of histiocytic sarcoma has not been described so far. In this article, we report three patients with HS, who were treated at the departement of Internal medicine, haematology and oncology, Faculty Hospital Brno. Despite the fact that all these patients had the same disease, the treatment effects differ depending on the stage of the disease at the time of diagnosis.