Background and Objective: Value-based payment programs link payments to the performance of providers on cost and quality of care to incentivize high-value care. To improve quality and lower costs, the Centers for Medicare and Medicaid Services (CMS) implemented the Quality Payment Program (QPP) for clinicians in 2017. Under the Medicare QPP, most eligible clinicians participate in one of the payment models: (a) Advanced Alternative Payment Models (A-APMs) through eligible APMs like Accountable Care Organizations (ACOs) or (b) the Merit-based Incentive Payment System (MIPS). ACO and MIPS clinicians participating in QPP differ in quality reporting requirements, and these differences are likely to affect the utilization of different quality measures, including preventive services. This study evaluated the differences in the utilization of preventive services by primary care clinicians participating in MIPS and ACOs., Methods: We use difference-in-difference regressions to compare preventive services in MIPS versus ACOs. Since preventive services like immunization and certain cancer screening are mandatory reporting measures for ACOs and voluntary measures for MIPS, the treatment group for this study is ACO clinicians and the comparison group is non-ACO MIPS clinicians. We obtained the rates of influenza immunization, pneumonia vaccination, tobacco use cessation intervention, depression screening, colorectal cancer screening, breast cancer screening, and wellness visits per 10 000 Medicare beneficiaries from Medicare Provider Utilization and Payment Public Use File (2012-2018)., Results: We had 508 144 total observations (ACO = 25.78% and MIPS = 74.22%) from 72 592 unique primary care clinicians. Compared to MIPS clinicians, ACO clinicians had significantly higher rates of pneumonia vaccination (incidence rate ratio [IRR] 1.25; 95% confidence interval [CI], 1.10-1.43) but lower rates of colorectal cancer screening (IRR 0.69; 95% CI, 0.50-0.96). Similarly, clinicians in ACO shared savings-only models had significantly higher rates of pneumonia vaccination (IRR 1.28; 95% CI, 1.11-1.48), depression screening (IRR 1.72; 95% CI, 1.09-2.71), and wellness visits (IRR 1.27; 95% CI, 1.09-1.47) compared to MIPS clinicians. There were no differences between ACO and MIPS clinicians on the utilization of breast cancer screening procedures and tobacco use cessation interventions., Conclusions: ACO clinicians may have prioritized relatively low-cost services such as pneumonia vaccination, depression screening, and wellness visits to improve their performance under QPP. Policymakers may need to alter incentives in performance-based payment programs to ensure that clinicians are improving all types of quality measures, including cancer screening., (Copyright © 2024 Wolters Kluwer Health, Inc. All rights reserved.)