BreastScreen Aotearoa (BSA) is the national breast screening programmen in New Zealand which aims to reduce cancer mortality through early diagnosis. The current research project is a population study which aims to evaluate the effects of national mammography screening on mortality from breast cancer in New Zealand. Specifically the research will measure whether there was a lower relative risk of breast cancer mortality in ever-screened versus unscreened women, with a dose-response effect in relation to recency and frequency of screening. The research includes two complementary studies: a retrospective population cohort study and a nested population-based case-control study of all women aged 50-69 years during the period 1999-2008. The population cohort study compares breast cancer mortality (the outcome) amoung groups with different screening histories (never, ever, or regularly screened) as the exposure variable. The case-control study compares the screening histories of all women who died of breast cancer (cases) during the study period, with the screening histories of a sample of those still alive (the controls). The studies include separate analyses for Maori, Pacific and Other women where numbers permit. The research requires national linkage of the New Zealand mammographic screening registers, the cancer register and the death register.