Medical State Assistance is a French public health insurance program that allows undocumented migrants to access primary, secondary, and tertiary care services free of user charge, either premium or out-of-pocket. The objective of this study is to assess the effect of Medical State Assistance on access to healthcare services and on usual source of care. The results show that undocumented migrants covered by Medical State Assistance are more likely to access outpatient healthcare services on both the intensive and the extensive margins. Moreover, undocumented migrants covered by Medical State Assistance are also more likely to report that primary care services are their usual source of care, in preference to emergency departments and other inpatient care services.