Most previous studies of graft-versus-host disease (GVHD) prophylaxis with methotrexate (MTX) alone in patients undergoing HLA-identical sibling donor bone marrow transplantation were performed in adults. With this background, we attempted to analyze the incidence and risk factors of GVHD in bone marrow transplantation (BMT) from an HLA-identical sibling donor in children with hematological malignancies using MTX alone as a prophylaxis for GVHD. Ninety-four patients received MTX by intravenous bolus injection, with a dose of 15 mg/m(2) on day +1, followed by 10 mg/m(2) on days +3, +6, and +11, and then weekly until day +60. The probability of developing grade II-IV acute GVHD and chronic GVHD was 19.1 and 31.8%, respectively. Age at transplantation and a female donor to male recipient were identified as risk factors for chronic GVHD in multivariate analysis, but no factors were identified for acute GVHD. The cumulative incidence of transplant-related mortality during the first 100 days was 9.6%. Disease-free survival at 5 years for standard- and high-risk patients was 82.1 and 39.5%, respectively. These results suggest that GVHD prophylaxis with MTX alone is safe and effective in young children under 10 years old at transplantation and in a setting other than female donor to male recipient.