The p53 tumor suppressor directs the cellular response to many mechanistically distinct DNA-damaging agents and is selected against during the pathogenesis of therapy-related acute myeloid leukemia (t-AML). We hypothesized that constitutional genetic variation in the p53 pathway would affect t-AML risk. Therefore, we tested associations between patients with t-AML (n = 171) and 2 common functional p53-pathway variants, the MDM2 SNP309 and the TP53 codon 72 polymorphism. Although neither polymorphism alone influenced the risk of t-AML, an interactive effect was detected such that MDM2 TT TP53 Arg/Arg double homozygotes, and individuals carrying both a MDM2 G allele and a TP53 Pro allele, were at increased risk of t-AML (P value for interaction is .009). This interactive effect was observed in patients previously treated with chemotherapy but not in patients treated with radiotherapy, and in patients with loss of chromosomes 5 and/or 7, acquired abnormalities associated with prior exposure to alkylator chemotherapy. In addition, there was a trend toward shorter latency to t-AML in MDM2 GG versus TT homozygotes in females but not in males, and in younger but not older patients. These data indicate that the MDM2 and TP53 variants interact to modulate responses to genotoxic therapy and are determinants of risk for t-AML.