Objective: To explore the influence of omission of the day +11 dose of methotrexate (MIX) on the incidence and severity of graft-versus-host disease (GVHD) after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Methods: From April 1997 to October 2002, 80 leukemia patients (46 men and 34 women aged from 12 to 56 years with a median age of 35) underwent allo-HSCT at our BMT unit. Among them, 58 patients received grafts from HLA-identical siblings, 8 from HLA one major antigen mismatched siblings and 14 from HLA-matched unrelated donors. All patients received a modified cyclosporine and short-course MTX regimen for GVHD prophylaxis, which included MTX 15 mg on day +1, and 10 mg on days +3 and +6 (MTX day +11 dose omitted) and cyclosporine given daily. Results: The overall incidence of grade I~IV acute GVHD was 57.5% (46/80 patients), with grade II~IV acute GVHD in 28 patients (35%) and grade III~IV acute GVHD in 7 patients (8.8%). Among 58 patients receiving grafts from HLA-identical siblings, 24 patients developed grade I~IV acute GVHD (41.4%), with grade II~IV acute GVHD in 13 patients (22.4%) and grade III~IV acute GVHD in 4 patients (6.9%). 2l out of 22 patients receiving grafts from HLA one major antigen mismatched siblings and HLA-matched unrelated donors developed grade I~IV acute GVHD (95.5%), with grade II~IV acute GVHD in 14 patients (63.6%) and grade III~IV acute GVHD in 3 patients (13.6%). Chronic GVHD occurred in 38 out of 56 evaluable patients (67.9%), with extensive form in 15 patients (26.8%) and limited form in 23 patients (41.1%). With a median follow-up of 960 days (range 180~1980 days), the probability of leukemia-free survival at 3 years was 61.3% for all patients. Conclusion: Our results suggest that the day +11 MTX can be omitted without a major deleterious effect on the incidence and severity of graft-versus-host disease after HLA-identical sibling transplantation as well as HLA one major antigen mismatched sibling and HLA-matched unrelated donor transplantation.