This paper examines the effect, by state, of the state's decision to adopt the Medicaid expansion. It also estimates the impact of the states decision on Medicaid enrollment and the number of uninsured. The paper shows that if all states implement the Affordable Care Act (ACA) Medicaid expansion, the federal government will fund the vast majority of the increase in Medicaid states. Due to several provisions of the ACA, states will face increased enrollment even if they do not implement the Medicaid expansion. The additional cost of implementing the expansion is small relative to total state spending without the expansion and relative to large increases in federal funding and current state budget expenditures.