The Patient Protection and Affordable Care Act (ACA) will expand access to affordable health insurance for millions of Americans. In states that choose to implement the Medicaid expansion for low-income adults, Medicaid will provide an important new pathway to coverage. Yet, even in states that choose to expand Medicaid a significant proportion of the low-income nonelderly adult population will be excluded from the Medicaid expansion due to their immigration status. Legal permanent residents, in most circumstances, are ineligible for Medicaid benefits for the first five years during which they reside legally in the U.S. and unauthorized immigrants are excluded from Medicaid coverage. This brief provides the first state-specific estimates of the number of uninsured low-income adults that will potentially be excluded from the Medicaid expansion because of their immigration status.