Background Health care reform is changing preventive services delivery. This study explored trajectories in colorectal cancer (CRC) testing over a 5-year period that included implementation of 16 Medicaid Accountable Care Organizations (ACOs, 2012) and Medicaid expansion (2014) – two provisions of the Affordable Care Act (ACA) - within the state of Oregon, USA. Methods Retrospective analysis of Oregon’s Medicaid claims for enrollee’s eligible for CRC screening (50–64 years) spanning January 2010 through December 2014. Our analysis was conducted and refined April 2016 through June 2018. The analysis assessed the annual probability of patients receiving CRC testing and the modality used (e.g., colonoscopy, fecal testing) relative to a baseline year (2010). We hypothesized that CRC testing would increase following Medicaid ACO formation – called Coordinated Care Organizations (CCOs). Results A total of 132,424 unique Medicaid enrollees (representing 255,192 person-years) met inclusion criteria over the 5-year study. Controlling for demographic and regional factors, the predicted probability of CRC testing was significantly higher in 2014 (+ 1.4 percentage points, p