The p53 protein and its regulator MDM2 is central to tumorigenesis by directing cells to undergo cell cycle arrest and/or apoptosis in response to DNA damage or other stress signals. The genes encoding these proteins contain nucleotide variation (p53 codon 72, MDM2 SNP309) that influences cellular response. We examined the p53 codon 72 and MDM2 SNP309 to determine their implication with age of disease onset and risk of breast cancer in young women (<or=36 years). No risk of breast cancer was observed for the genotypes of p53 and MDM2, however, a tendency (P=0.15) towards increased risk of early onset breast cancer was observed in carriers of two or more Pro and/or G alleles. We further calculated the influence on age at diagnosis. Cases were grouped according to the number of G and Pro alleles (0, 1, 2 or 3-4) and age at diagnosis. A significant trend towards decreased age at diagnosis with increased number of risk alleles was found (P=0.013). Our results suggest that p53 codon 72 and MDM2 SNP309 may be implicated in early onset breast cancer.