Certain cytokine genotypes are associated with acute graft versus host disease (aGVHD) after bone marrow transplantation (BMT). The present study aimed to determine existing association between TGF-beta1 codon 10 polymorphism and aGVHD after HLA-identical sibling BMT in the Iranian population. In a retrospective case-control study, 168 subjects including 84 Iranian HLA-identical sibling BMT donor/recipient pairs were recruited. All of the patients were affected by hematological malignancies (AML=39, ALL=23 and CML=22). PCR-SSP method was performed to determine TGF-beta1 codon 10 T/C polymorphism genotypes. The frequency of TGF-beta1 codon 10 TT, TC and CC genotypes among all subjects were 26.8%, 33.3% and 39.9% respectively. Recipients with the T allele developed aGVHD significantly less than those without the T allele (odds ratio =0.334, P=0.026). Genetic background of TGF-beta1 may be involved as a protective factor in the development of aGVHD in HLA-matched sibling BMT in Iranian population. Moreover, this finding may indicate that the genetic markers in Iranians are, at least to some extent, linked to distinct genetic event from Japanese.