Aims This retrospective, population-based study investigated the patterns and risks of mortality from breast cancer, other cancers and non-cancer causes according to the age at diagnosis of breast cancer. Methods Mortality was assessed in all Australian women (n?=?179?653) aged 30-79 years who were diagnosed with breast cancer between 1982 and 2004 and who survived a minimum of 1?year. The mean follow up was 6.3?years (range 0-23?years). Results Before December 2005, 52?934 women had died (34?459 of breast cancer, 5019 of other cancers and 13?456 of non-cancer causes). There was an inverse age-related relative risk of mortality (calculated as the standardized mortality ratio [SMR]) from breast cancer (linear trend across age P?<?0.01). For breast cancer survivors the age-adjusted SMR was 0.99 for other cancers and 0.81(P?<?0.01) for non-cancer causes in comparison with the general population. The SMR for other cancers and non-cancer causes was highest in the 30-39-year-old age group (2.13, P?<?0.01 and 2.15, P?<?0.01, respectively), and progressively decreased with increasing age, with the 70-79-year-old age group having significantly reduced SMR (0.95, P?<?0.05, and 0.78, P?<?0.01, respectively, compared with the age-matched general population). Conclusion There was an inverse age-related relative risk of death from breast cancer, other cancers and non-cancer causes. These findings suggest that younger Australian women require long-term health surveillance and that older women with limited comorbidities require optimal treatment of their breast cancer.