A large presacral myelolipoma associated with increasing constipation is reported in a 70-year-old obese diabetic female. The resected tumor was encapsulated and dark red to yellow. Light and electron microscopy revealed mature and immature hematopoietic tissue, lymphoid aggregates and mature adipocytes. Myelolipomas arising in extra-adrenal sites are rare. Considered in the differential diagnosis are reactive extramedullary hematopoietic tumors that usually occur in patients with severe chronic anemias. Patients with extramedullary hematopoietic tumors are characterized by anemia, frequent hepatosplenomegaly and abnormal peripheral blood smears, and may be any age. The tumors are usually multiple and usually located in the mediastinum or epidural space. In contrast, patients with extra-adrenal myelolipomas are usually older than 40 years, have normal blood studies, absent hepatosplenomegaly, and usually have chronic debilitating diseases or endocrinopathies. Extra-adrenal myelolipomas are single and usually occur within the abdomen. Extramedullary hematopoietic tumors have a predominance of the hematopoietic component, with erythroid hyperplasia of that component. Extra-adrenal myelolipomas may have a predominance of either the hematopoietic or fatty component, chiefly the latter, and generally have a more conspicuous lymphocyte population. Although the components of these tumors are the same, we consider them separable clinically, pathogenetically and, in many cases, pathologically.