This paper examines how changes in Medicaid physician payments affect provision of care to both Medicaid patients and the uninsured. I find that payment increases generate an increase in supply of care to Medicaid patients but a more than offsetting decrease in supply to the uninsured. Using survey data, I additionally show that physicians encourage their uninsured patients to enroll in Medicaid. Finally, I demonstrate that when Medicaid eligibility is high, physicians are less likely to substitute between caring for Medicaid patients and treating the uninsured. Because higher eligibility magnifies the Medicaid supply response to a payment change, my results suggest that payment increases should be coupled with eligibility expansions in order to improve access to care among the poor.