Medicaid and the Children's Health Insurance Program (CHIP)--two joint federal-state health care programs for certain low-income individuals--play a critical role in addressing the health care needs of children. The Children's Health Insurance Program Reauthorization Act of 2009 required GAO to study children's access to care under Medicaid and CHIP, including information on physicians' willingness to serve children covered by Medicaid and CHIP. GAO assessed (1) the extent to which physicians are enrolled and serving children in Medicaid and CHIP and accepting these and other children as new patients, and (2) the extent to which physicians experience difficulty referring children in Medicaid and CHIP for specialty care, as compared to privately insured children. GAO conducted a national survey of nonfederal primary and specialty care physicians who serve children, and asked about their enrollment in state Medicaid and CHIP programs, whether they served and accepted Medicaid and CHIP and privately insured children, and the extent to which they experienced difficulty referring children in Medicaid and CHIP and privately insured children to specialty care. GAO also interviewed officials with the Centers for Medicare & Medicaid Services (CMS), an agency within the Department of Health and Human Services (HHS) that oversees Medicaid and CHIP.