Abstract Purpose: The germ-line polymorphisms TP53 Arg72Pro and MDM2 SNP309 T>G are risk factors for tumor development and affect response to chemotherapy and survival in several cancers, but their prognostic and predictive value in patients with high-grade osteosarcomas is not yet defined. The purpose of this study was to investigate the effect of the TP53 Arg72Pro and the MDM2 SNP309 on the risk of osteosarcoma development and survival. Experimental Design: The relative risk to develop osteosarcomas and the overall survival associated to TP53 Arg72Pro and MDM2 SNP309 polymorphisms were investigated in 201 patients. Correlations with event-free survival (EFS) were analyzed in a homogeneous subgroup of 130 patients with high-grade osteosarcomas of the limbs, nonmetastatic at diagnosis, which underwent neoadjuvant chemotherapy. Results: Multivariate analysis showed that the MDM2 polymorphism T309G was associated with an increased risk of developing osteosarcomas [GG versus TT; odds ratio, 2.09; 95% confidence interval (95% CI), 1.15-3.78]. A case/control gender approach evidenced a significant increased risk only for female osteosarcoma patients (GG versus TT; odds ratio, 4.26; 95% CI, 1.61-11.25). Subjects carrying the TP53 Arg72Pro polymorphism were found to have a significantly increased death risk (Pro/Pro versus Arg/Arg; hazard ratio, 2.90; 95% CI, 1.28-6.66). In the subgroup of 130 high-grade osteosarcomas, the TP53 Arg72Pro was an independent marker of EFS (Pro/Pro versus Arg/Arg; hazard ratio, 2.67; 95% CI, 1.17-6.11). Conclusion: The study provides evidence supporting the association of MDM2 SNP309 with high-grade osteosarcoma risk in females and shows that TP53 Arg72Pro has a prognostic value for overall survival and EFS in osteosarcoma patients.