As part of the Affordable Care Act, primary care physicians providing services to patients insured through Medicaid in some states will receive higher payments in 2013 and 2014 than in the past. Payments for some services will increase to match Medicare rates. This change may lead to wider acceptance of new Medicaid patients among primary care providers. Using data from the 2011–12 National Ambulatory Medical Care Survey Electronic Medical Records Supplement, I summarize baseline rates of acceptance of new Medicaid patients among office-based physicians by specialty and practice type. I also report state-level acceptance rates for both primary care and other physicians. About 33 percent of primary care physicians (those in general and family medicine, internal medicine, or pediatrics) did not accept new Medicaid patients in 2011–12, ranging from a low of 8.9 percent in Minnesota to a high of 54.0 percent in New Jersey. Primary care physicians in New Jersey, California, Alabama, and Missouri were less likely than the national average to accept new Medicaid patients in 2011–12. The data presented here provide a baseline for comparison of new Medicaid acceptance rates in 2013–14.