Cytotoxic T-lymphocyte antigen 4 (CTLA-4) is an important protein involved in the regulation of theimmune system. The +49 G/A polymorphism is the only genetic variation in the CTLA-4 gene that causes anamino acid change in the resulting protein. It is therefore the most extensively studied polymorphism among allCTLA-4 genetic variants and contributions to increasing the likelihood of developing cancer are well known invarious populations, especially Asians. However, there have hiterto been no data with respect to the effect of thispolymorphism on breast cancer susceptibility in our North Indian population. We therefore assayed genomicDNA of 250 breast cancer subjects and an equal number of age-, sex- and ethnicity-matched healthy controlsfor the CTLA-4 +49 G/A polymorphism but no significant differences in either the gene or allele frequency werefound. Thus the CTLA-4 +49 G/A polymorphism may be associated with breast cancer in other Asians, but itappears to have no such effect in North Indians. The study also highlights the importance of conducting geneticassociation studies in different ethnic populations.