Graft-versus-host disease (GVHD) is an important complication of allogeneic bone marrow transplantation (BMT). To assess its influence on transplant outcome, we studied 90 Chinese patients with hematologic disorders with BMT from HLA-identical siblings. GVHD prophylaxis consisted of a combination of methotrexate (MTX) and cyclosporine A (CsA). The incidence of grade II-IV acute GVHD was 29% (95% CI 19-38%). The incidence of limited and extensive chronic GVHD was 30% (95% CI 20-40%). For patients transplanted for early hematologic malignancy (n = 40), those with GVHD (acute and/or chronic) had lower relapse rate (17% (95% CI 0-36%) vs. 54% (95% CI 26-82%), P = 0.043). They had higher transplant-related mortality (12% (95% CI 0-28%) vs. 6% (95% CI 0-18%), P = 0.715) and event-free survival (EFS) (73% (95% CI 53-93%) vs. 43% (95% CI 17-69%), P = 0.104) that had not reached statistical significance. For patients transplanted for advanced hematologic malignancy (n = 37), those with GVHD also had lower relapse rate (5% (95% CI 0-15%) vs. 72% (95% CI 50-94%), P = 0.002) and higher transplant-related mortality (50% (95% CI 27-73%) vs. 8% (95% CI 0-24%), P = 0.006) than those without any GVHD. They had higher EFS (47% (95% CI 24-70%) vs. 26% (95% CI 5-47%), P = 0.609) that had not reached statistical significance. Therefore, the incidence of acute and chronic GVHD in Chinese was similar to that of their Caucasian counterparts using MTX and CsA for GVHD prophylaxis.(ABSTRACT TRUNCATED AT 250 WORDS)