Background. Older adults with limited life expectancy frequently receive cancer screening, although on average, harms outweigh benefits. We examined the influence of life expectancy on older adults' cancer screening decisions relative to three other factors. Methods. Adults aged 65+ years (N = 1272) were recruited from a national online survey panel. Using a discrete choice experiment, we systematically varied a hypothetical patient's life expectancy, age, quality of life, and physician's recommendation and asked whether the participant would choose screening. Participants were randomized to questions about colonoscopy or prostate-specific antigen/mammography screenings. Logistic regression produced preference weights that quantified the relative influence of the 4 factors on screening decisions. Results. 879 older adults completed the survey, 660 of whom varied their screening choices in response to the 4 factors we tested. The age of the hypothetical patient had the largest influence on choosing screening: the effect of age being 65 versus 85 years had a preference weight of 2.44 (95% confidence interval [CI]: 2.22, 2.65). Life expectancy (10 versus 1 year) had the second largest influence (preference weight: 1.64, CI: 1.41, 1.87). Physician recommendation (screen versus do not screen) and quality of life (good versus poor) were less influential, with preference weights of 0.90 (CI: 0.72, 1.08) and 0.68 (CI: 0.52, 0.83), respectively. Conclusions. While clinical practice guidelines increasingly use life expectancy in addition to age to guide screening decisions, we find that age is the most influential factor, independent of life expectancy, quality of life, and physician recommendation, in older adults' cancer screening choices. Strategies to reduce overscreening should consider the importance patients give to continuing screening at younger ages, even when life expectancy is limited.