An updated analysis of the impact of the Affordable Care Act (ACA) on uninsured health center patients estimates that 1.1 million community health center patients are left without the benefits of health coverage simply because they live in one of 24 states that have opted out of the Medicaid expansion. The vast majority (71 percent) of the 1.1 million patients left behind live in just 11 southern states (AL, FL, GA, LA, MS, NC, OK, SC, TN, TX, VA). The analysis also shows that health centers in the opt-out states will likely forgo over half a billion dollars in revenues they would have received under a Medicaid expansion. The loss of potential revenues presents significant challenges to these health centers, which already struggle to care for rising numbers of uninsured patients. The brief is authored by Peter Shin, PhD, MPH Jessica Sharac, Msc, MPH, and Sara Rosenbaum, JD of the Geiger Gibson/RCHN Community Health Foundation Research Collaborative at the Milken Institute School of Public Health (Milken Institute SPH) at the George Washington University.