The P53 tumor suppressor pathway plays an important role in cancer development. The auto-regulatory feedback mechanism of the P53 and MDM2 expression is critical in keeping proper tumor suppressor function of this pathway. This study examined the effect of P53 Arg72Pro variants on transactivation of polymorphic MDM2 promoter (T309G) and their associations with risk of developing gastric cardia adenocarcinoma (GCA) in a Chinese population. Luciferase assays consistently showed a significantly higher activity of the MDM2 309G promoter compared with the MDM2 309T promoter. In cells co-transfected with variant P53 cDNAs, P53-72Pro displayed a significantly higher ability to activate the MDM2 promoter than P53-72Arg. Genotype analyses in 500 GCA patients and 1000 controls showed that significantly increased risk for developing GCA was associated with the MDM2 309G and the P53 72Pro allele compared with the MDM2 309T and the P53 72Arg allele in an allele dose-dependent manner. A joint effect between the MDM2 and P53 polymorphisms in intensifying GCA risk was detected, with the odds ratio (OR) for the presence of both MDM2 390GG and P53 72Pro/Pro genotypes being 5.05 [95% confidence interval (CI), 2.50-10.20]. These results suggest that the P53 72Pro and MDM2 309G polymorphisms contribute to the risk of developing GCA.