Sclerosing extramedullary hematopoietic tumor (SEMHT) occasionally may arise in patients with chronic myeloproliferative disorders (CMPDs). Morphologically, these tumors may be mistaken for sarcomas or other neoplasms, especially if the clinical history is unknown. We analyzed four cases to identify features to aid in this differential diagnosis. Clinically, there were four men (mean age, 64.5 years), each with a history of CMPD. Grossly, the SEMHTs formed solitary renal or perirenal masses or multiple mesenteric or omental nodules. Morphologically, each SEMHT had a sclerotic to myxoid background with thick collagen strands and trapped fat. Atypical megakaryocytes, maturing granulocytic and erythroid precursors, and few to no blasts were identified in all cases. The megakaryocytes, granulocytic precursors, and erythroid precursors reacted strongly with antibodies to factor VIII, myeloperoxidase, and hemoglobin, respectively, in immunohistochemical studies performed in selected cases. SEMHT is a rare manifestation of CMPD that may be mistaken for a sarcoma, especially sclerosing liposarcoma, Hodgkin's disease, especially lymphocyte depletion type, or a myelolipoma. In a myxoid tumor with trapped fat and atypical cells, morphologic and immunohistochemical identification of maturing hematopoietic precursors helps distinguish SEMHT from sarcoma or Hodgkin's disease. The presence of sclerosis and atypical megakaryocytes helps distinguish SEMHT from myelolipoma.