OBJECTIVE : The purpose of the study is to examine relationships between long-term trends of region- and age-specific rates of mammography, hormone replacement therapy (HRT), and breast cancer incidence and mortality in Canadian women aged 35 years and older. METHODS : Population-based complex surveys were used to estimate mammography use in the past 2 years and ever, and HRT use in the past month. National population-based administrative data were used to estimate breast cancer incidence and mortality. Joinpoint analyses were used to estimate trends in rates and years where trend changed. RESULTS : No consistent relationship between mammography use and breast cancer incidence was observed across age groups. Opportunistic screening occurred prior to the establishment of organized screening programs in Canada and prior to substantial declines in breast cancer mortality observed around 1990. Women aged 35-39 years demonstrated a 62.8% relative decrease in breast cancer mortality between 1950 and 2015 despite lower rates of mammography use in the past 2 years (range 9.4-15.9%) reinforcing important treatment advances. A substantial proportion of women in their 40s report mammography use in the past 2 years (range 35.8-42.2%) and regional variation exists reflecting inconsistencies in guidelines across Canada. CONCLUSIONS : Rates of mammography use over time do not necessarily reflect national guideline releases or establishment of organized screening programs.