We report long-term outcomes of 329 childhood severe aplastic anemia (SAA) patients who underwent hematopoietic SCT (HSCT) from an HLA-matched sibling donor in the Japanese Hematopoietic Cell Transplantation Registry. OS and EFS at 10 years were as high as 89.7 þ / À 1.7% and 85.5 þ / À 2.0%, respectively. Five cases of late malignancies (LM) were identified (malignant peripheral nerve sheath tumor, thyroid carcinoma, colon carcinoma, MDS and hepatoblastoma). Cumulative incidence of LM was 0.8% at 10 years and 2.5% at 20 years, respectively, which was lower than that in previous reports. This low incidence is in keeping with the low occurrence of skin cancer in Japanese population and of acute GVHD in our study group. Radiation-containing conditioning was not significantly associated with the incidence of LM after HSCT probably because of absolute low patient number who developed LM in our series. In terms of LM development after HSCT, low-dose TBI in HSCT for SAA to avoid graft rejection, which is commonly used in Japan, might be tolerable in the Japanese population because of its low incidence. Keywords: aplastic anemia; childhood; hematopoietic SCT; long-term outcome; late malignancies INTRODUCTION Aplastic anemia is a hematopoietic disorder characterized by pancytopenia and BM hypoplasia. Therapeutic options for severe aplastic anemia (SAA) are immunosuppressive therapy and hematopoietic SCT (HSCT). In children, if an HLA-matched sibling donor (MSD) is available, HSCT is the first line of therapy for SAA. HSCT from MSD is an established standard therapy for SAA in children and high survival rates have already been reported. However, little is known about long-term outcomes of these children.Late malignancies (LM) are serious complications for patients who undergo HSCT. 3,4 In SAA, LM are also reported in the patients with HSCT and its occurrence is related to radiation-containing conditioning regimen and GVHD grade in adults, 5,6 however, the incidence and prognostic factors of LM in children with SAA who undergo HSCT are totally unknown.In this article, we report long-term outcomes of childhood SAA patients who underwent HSCT from MSD in the centers of the Japanese Hematopoietic Cell Transplantation Registry and describe the occurrence of LM.