BACKGROUND: Potential benefits of screening mammography among women ages 75 years and older remain unclear. METHODS: We evaluated 10-year cumulative incidence of breast cancer and death from breast cancer and other causes by Charlson Comorbidity Index (CCI) and age in the Medicare-linked Breast Cancer Surveillance Consortium (1999-2010) cohort of 222 088 women with no less than 1 screening mammogram between ages 66 and 94 years. RESULTS: During median follow-up of 107 months, 7583 were diagnosed with invasive breast cancer and 1742 with ductal carcinoma in situ; 471 died from breast cancer and 42 229 from other causes. The 10-year cumulative incidence of invasive breast cancer did not change with increasing CCI but decreased slightly with age: ages 66-74 years (CCI0 = 4.0% [95% CI = 3.9% to 4.2%] vs CCI  ≥ 2 = 3.9% [95% CI = 3.5% to 4.3%]); ages 75-84 years (CCI0 = 3.7% [95% CI = 3.5% to 3.9%] vs CCI  ≥ 2 = 3.4% [95% CI = 2.9% to 3.9%]); and ages 85-94 years (CCI0 = 2.7% [95% CI = 2.3% to 3.1%] vs CCI  ≥ 2 = 2.1% [95% CI = 1.3% to 3.0%]). The 10-year cumulative incidence of other-cause death increased with increasing CCI and age: ages 66-74 years (CCI0 = 10.4% [95% CI = 10.3 to 10.7%] vs CCI ≥ 2 = 43.4% [95% CI = 42.2% to 44.4%]), ages 75-84 years (CCI0 = 29.8% [95% CI = 29.3% to 30.2%] vs CCI ≥ 2 = 61.7% [95% CI = 60.2% to 63.3%]), and ages 85 to 94 years (CCI0 = 60.3% [95% CI = 59.1% to 61.5%] vs CCI  ≥ 2 = 84.8% [95% CI = 82.5% to 86.9%]). The 10-year cumulative incidence of breast cancer death was small and did not vary by age: ages 66-74 years = 0.2% (95% CI = 0.2% to 0.3%), ages 75-84 years = 0.29% (95% CI = 0.25% to 0.34%), and ages 85 to 94 years = 0.3% (95% CI = 0.2% to 0.4%). CONCLUSIONS: Cumulative incidence of other-cause death was many times higher than breast cancer incidence and death, depending on comorbidity and age. Hence, older women with increased comorbidity may experience diminished benefit from continued screening.