Dear Editor, A 49-year-old man presented with abdominal distension, weight loss of 6 kg, night sweats, fever, and a compromised condition for about 1 month. A computed tomography (CT) scan revealed a large retroperitoneal mass, and the suspected diagnosis was non-Hodgkins lymphoma. At admission, physical examination revealed hepatosplenomegaly without peripheral lymph node enlargement. Several biopsies for histopathologic evaluation were performed. The diagnosis of soft tissue sarcoma (malignant fibrous histiocytoma) was made and polychemotherapy with epirubicin, ifosfamide, and etoposide (without cisplatinum because of tumorassociated hydronephrosis with concomitant renal impairment) was initiated. Immunohistopathological reevaluation showed xanthogranulomatous inflammation (Figs. 1 and 2) with multinuclear giant cells and foamy histiocytes positive for CD68 (Fig. 3) and CD45, but the absence of CD1a immunoreactivity (excluding a Langerhans cell histiocytosis). The diagnosis of non-Langerhans-histiocytosis Erdheim–Chester disease (ECD) was made and confirmed by an international reference pathologist. A bone scan with 99mTc-MDP showed the typical increased bilateral symmetric uptake within the long bones sparing the epiphyses. Pathognomonic radiographic findings were bilateral symmetric osteosclerosis of the long bones and lytic bone changes localized especially in the metaphyses (Fig. 4). Histological examination of lung and bone marrow confirmed the diagnosis of ECD. Neither treatment with the cytotoxic drug eldesine and prednisolone nor high dose dexamethasone was of any beneficial effects. The patient developed multi-organ failure, severe anemia, and thrombocytopenia. Bone marrow examination showed multiple histiocytic cells showing extensive hemophagocytosis (Figs. 5 and 6). The patient died 4 months after admission. Erdheim–Chester disease is a rare non-Langerhans’ form of histiocytosis first described by William Chester in 1930. Until now, less than 100 cases have been published in the literature. ECD lesions are characterized by infiltrates of xanthomatous histiocytes positive for CD68, in contrast to Langerhans-cell lineage negative for CD1a and S100, Birbeck granules are not found. The presence of a monoclonal cell population cannot be detected by the HUMARA assay [1]. The pathognomonic radiological findings are symmetric. Diaphyseal or metaphyseal sclerotic lesions are found in the long bones, mainly the femur, the tibia, and the fibula. Bone pain is the most frequent symptom. General symptoms such as fever, weight loss, and weakness are reported. Extraskeletal manifestations have been found in the lung (35%), pericardium, myocardium, aorta, orbita (26%), retroperitoneum (37%), skin, and CNS (30%) [2]. The prognosis of ECD is grim. In a retrospective analysis by Veyssier-Belot et al. [2], 22 from 59 patients died after a Ann Hematol (2007) 86:847–849 DOI 10.1007/s00277-007-0324-4