This presentation discusses new measures of provider participation in Medicaid based on a new data set that uses claims and encounter data to identify physicians serving Medicaid patients. Preliminary results represent the first of several planned analyses using practitioner data to improve the evidence based on access to care for Medicaid beneficiaries. Participation measures are presented for physicians in selected specialties in 34 states. In addition, the presentation contains new information on other advanced practice and other health care professionals serving Medicaid patients.