We report our single-center experience with related allogeneic bone marrow transplantation (BMT) in pediatric recipients between April 1998 and December 2004. Allogeneic bone marrow grafts from 19 donors (18 human leukocyte antigen (HLA)-matched sibling donors and 1 one antigen-mismatched related donor) were transplanted into patients aged 3-17 years (16 with leukemia and 3 with non-malignant disease). The patients received a cell dose, with median total nucleated cell dose of 3.9 x 10(8)/kg (range, 0.7 - 8.7 x 10(8)) and median CD 34+ cell dose of 3.0 x 10(6)/g (range, 0.3 - 9.8 x 10(6)). Seventeen patients (89.4%) engrafted after a median of 19 days (range 14-20 days). Acute graft versus host disease (GVHD) grade II to IV developed in 8 patients (42. 1%), and limited chronic GVHD developed in 2 evaluable patients (10.5%). Twelve of the 19 patients were alive at a median follow-up of 1460 days (range, 270-2260 days). Full chimeric hematopoiesis was maintained in 11 of these 12 patients. Six patients (31.6%) had relapse of their underlying malignant disease, and one of them is still alive. Seven patients died (5 because of relapse and/or disease progression and 2 because of infectious complication). The underlying diseases were acute lymphoblastic leukemia (ALL; 4 cases: 3 CR2, 1 Ph+), acute myeloid leukemia (AML; 2 cases: 1 CR2, 1 refractory), and juvenile chronic myelogenous leukemia (JCML; 1 case). Relapsed leukemia at an extramedullary site occurred in 2 patients with ALL after BMT. Although our data should be interpreted cautiously considering the limited number of patients, isolated extramedullary relapse seems to be common after allogeneic BMT.