The Affordable Care Act (ACA) helped make preventive care, including recommended cancer screening, more affordable and accessible for millions of Americans. Using population-based data from the Surveillance, Epidemiology, and End Results (SEER) Program, we estimated the impact of ACA policy changes to facilitate the diagnosis of cancer at an earlier and more treatable stage. We estimated that the ACA resulted in an increase of 8,400 (8 percent) diagnoses of early-stage colorectal cancer among US seniors in the period 2011–13. However, the ACA had no distinguishable effect on the number of diagnoses of early-stage breast cancer over the same time period. It is likely that the ACA initially affected the diagnosis of colorectal cancer more than that of breast cancer because the decrease in out-of-pocket spending was larger for colorectal than for breast cancer screening.