The aim of this case-control study was to investigate whether the common G870A polymorphism in the Cyclin D1 gene (CCND1) is a risk factor for breast and colorectal cancers in an Australian population.,A total of 339 breast and 569 colorectal cancer cases were studied, together with 327 age-matched controls. Genotyping for the G870A polymorphism in CCND1 was carried out using single strand conformation polymorphism and Pyrosequencing methods.,Comparison of the CCND1 G870A genotype frequencies revealed no significant associations between presence of the A allele and the risk of either breast or colorectal cancer. No associations were noted between presence of the A allele and pathological features of these tumours or patient survival.,Although the CCND1 G870A polymorphism has been reported as a genetic risk factor for some tumour types, it does not appear to be linked to the risk of breast and colorectal cancers.