There has been a 28% reduction in age-standardised breast cancer mortality in Australia since 1991 when the free national mammographic program (BreastScreen) began. Therefore, a comparative study between BreastScreen participation and breast cancer age specific mortality trends in Australia was undertaken for two time periods between 1991 and 2007, where women aged 50-59 and 60-69 years, who were invited to screen, were compared to women aged 40-49 and 70-79 years who were not invited, but who did have access to the program. There were mortality reductions in all four age groups between 1991-1992 and 2007, resulting in 5,849 (95% CI 4,979 to 6,718) fewer women dying of breast cancer than would have otherwise been the case. Women aged 40-49 years, who had the lowest BreastScreen participation (approximately 20%), had the largest mortality reduction: 44% (95% CI 34.8-51.2). Women aged 60-69 years, who had the highest BreastScreen participation (approximately 60%), had the smallest mortality reduction: 19% (95% CI 10.5-26.9). As BreastScreen participation by invited women aged 50-69 years only reached a maximum of about 55-60% in 1998-1999, a decline in mortality in Australian women cannot be attributed to BreastScreen prior to this time. Thus, almost 60% of the Australian decline in breast cancer mortality since 1991 cannot be attributed to BreastScreen. Therefore, mammographic screening cannot account for most of the reductions in breast cancer mortality that have occurred in Australian women since 1991 and may have contributed to over-diagnosis. Most, if not all, of the reductions can be attributed to the adjuvant hormonal and chemotherapy, which Australian women have increasingly received since 1986.