As part of the Affordable Care Act, states had the ability to expand Medicaid coverage from 100% of the federal poverty line to 138%. I analyze whether this state voluntary Medicaid expansion increased Medicaid coverage without causing private insurance crowd-out. I also examine whether this expansion reduced medical out-of-pocket payments. I use a difference-in-differences estimator to compare states that expanded in early 2014 and states that chose not to expand their Medicaid coverage. I find that states that expanded saw a statistically significant 4.6 percentage point increase in Medicaid coverage relative to non-expansion states, with no evidence of crowd-out. I also find that medical out-of-pocket payments decreased in expansion states.