True histiocytic lymphoma (THL) is an uncommon type of non-Hodgkin lymphoma (NHL), the malignant cells of which originate from phagocytic histiocytes [1]. Using only histopathologic study, the diagnosis of THL has frequently been misinterpreted [2]. However, by the application of immunophenotypic technique for studying different cell lineages, many previously diagnosed THL have turned out to be Ki-1-positive anaplastic large cell lymphoma and high grade lymphoma of B or T cell origin [2,3]. The criteria generally used for diagnosis of THL is the reactivity of the malignant cells with the monocytemacrophage markers and lack of reactivity with B-and T-cell markers [2][3][4]. Using such immunophenotypic criteria, the incidence of THL studied retrospectively is only 0.2-0.6% of all cases of NHL [3,[5][6][7][8]. The common clinical feature of THL is a localized tumor that may or may not be disseminated. The usual organs of involvement are the skin, lymph nodes, gastrointestinal tract, and soft tissues [9][10][11][12]. Recently, the disease was reported to be a second tumor following completed treatment of lymphoblastic neoplasms [13]. Herein we report an additional patient with THL manifested during the maintenance chemotherapy for acute lymphoblastic leukemia (ALL).She was an 8-year-old girl who presented with a 2-week history of limping, low grade fever, and bruises. Hepatosplenomegaly, generalized lymphadenopathy and petechiae and ecchymoses on trunk and extremities were found on physical examination. The complete blood count showed hemoglobin 91.0 gm/L, white blood cells 41.3 Â 10 9 /L, 69% of which were blast cells and platelet count 88.0 Â 10 9 /L. Lymphoblasts of L 2 (FAB) morphology with positive PAS staining were found in bone marrow aspirate. The immunophenotypes revealed 10 and 5% positive CD 8 and CD 2 markers respectively. She was treated with the modified Children Cancer Study Group protocol for ALL with good response. Six months later, she developed right hip pain. An osteolytic lesion was found in the right upper femur on plain film. The whole body bone scan showed multiple areas of increased radioactivity in the right upper femur, right acetabulum, distal left femur, the left seventh posterior rib, distal left humerus, and both pubic bones. Bone biopsy of the right femur was reported to be benign fibrous histiocytoma. She was continued on the maintenance phase of chemotherapy for ALL. Four months later, she developed pain in the back and weakness of the lower extremities. MRI of the whole spine showed an extradural mass at T8-10 level with cord compression. She went on T8-10 laminectomy and total tumor removal. The pathologic report was THL with positive CD 68 marker and negative myeloperoxidase, LCA, CD 45, CD 3, CD 45 RO, CD 20, and S100 markers (Fig. 1). The electron microscopic study confirmed the diagnosis of histiocytic lymphoma. She was treated with the CHOP protocol. The tumor partially responded. A few months later, the tumor recurred locally and additional tumor masses were found in the lef...