PURPOSE: Although guidelines recommend that clinicians consider life expectancy before screening older women for breast cancer, mammography is not targeted to the oldest women in good health and most likely to benefit. We aimed to identify factors important to women aged 80+ mammography screening decisions compared to women aged 65-79. METHODS: We conducted telephone surveys of 107 women aged 80+ and 93 women aged 65-79 randomly selected from one academic primary care practice who were able to communicate in English (59% response rate). The survey assessed: perceived importance of a history of breast disease, family history of breast cancer, doctor's recommendations, habit, reassurance, previous experience, mailed reminder cards, family/friend's recommendations or experience with breast cancer, age, health, and media, in elderly women's mammography screening decisions. The survey also assessed older women's preferred role in decision making around mammography screening. RESULTS: Of the 200 women, 53.5% were aged 80+ and 46.5% were aged 65-79. The majority were non-Hispanic white (65.5%) and were in good to excellent health (82.8%). Most (81.3%) had undergone mammography in the past 2 years. Regardless of age, elderly women ranked doctor's recommendations as the most important factor influencing their decision to get screened. Habit and reassurance were the next two highly ranked factors for all women. Among women who did not get screened, women aged 80+ ranked age and doctor's counseling as the most influential factors and women aged 65-79 ranked previous negative experience with mammography as the most important factor. Women aged 80+ (32.0%) were more likely to prefer that their doctor make the final decision about whether or not they undergo mammography screening than women aged 65-79 (21.5%). However, many women in both age groups preferred to make the final decision on their own (46.6% of women aged 80+ and 50.5% of women aged 65-79). Women aged 80+ who preferred to share decision-making with their clinician were less commonly screened than other women. CONCLUSION: While a doctor's recommendation is the most important factor influencing elderly women's mammography screening decisions, habit and reassurance also strongly influence decision-making. Interventions aimed at improving clinician counseling about mammography with older women, which include discussions around habit and reassurance, may result in more meaningful decision-making.