Histiocytic sarcoma (HS) is a rare malignant neoplasm of the lymphohematopoietic system, that occurs in lymph nodes, skin and at extranodal site, particularly the gastrointestinal tract. Although it shows characteristic histologic and immunohistochemical features, it may be misdiagnosed. We report a 67-year-old female patient with colicky abdominal pain and vomiting. A CT scan of the abdomen reveled a tumour in the ileum. At laparotomy a mass in the small intestine was removed. The neoplastic cells displayed large abundant eosinophilic cytoplasm, with bizarre-shaped nuclei, and expressed CD 45, CD 68 and lisozyme. The diagnosis of HS requires the use of a panel of immunohistochemical markers and may be supported by ultrastructural findings.