PURPOSE: Accountable care organizations (ACOs) are a delivery and payment model designed to encourage integrated, high-value care. We designed a study to test the association between ACOs and two recommended cancer screening tests, colonoscopy for colorectal cancer and mammography for breast cancer. METHODS: Using the random 20% sample of Medicare claims, beneficiaries were attributed to ACO or non-ACO cohorts on the basis of providers' enrollment in the Medicare Shared Savings Program. An inverse probability of treatment weighting was used to balance patient characteristics between ACO and non-ACO cohorts. A propensity score-weighted, difference-in-differences analysis was then performed using the same provider groups in 2010-pre-ACO-as a baseline. A secondary analysis for older-nonrecommended-age ranges was performed. RESULTS: Prevalence of colonoscopy in recommended age ranges in ACOs from 2010 to 2014 increased from 15.3% (95% CI, 14.9% to 15.6%) to 17.9% (95% CI, 17.3% to 18.5%). This differed significantly from the change in non-ACOs (difference in differences, 1.2%; P < .001). Among women in ACOs, mammography prevalence rose from 53.7% (95% CI, 53.0% to 54.4%) to 54.9% (95% CI, 54.2% to 55.7%). In contrast to colonoscopy, the difference in mammography prevalence was not significantly different in ACO versus non-ACOs (difference in differences, 0.49%; P < .13). A similar pattern was also observed in older-nonrecommended-age ranges with significant difference in differences (ACO v non-ACO) in colonoscopy, but not mammography. CONCLUSION: The impact of ACOs on cancer screening varies between screening tests. Our results are consistent with a greater effect of ACOs on high-cost, high-complexity screening services, which may be more sensitive to integrated care delivery models.