Starting in 2014, many low-income adult residents of states that forgo the Affordable Care Act’s expansion of Medicaid would be eligible for that program if they moved to a state that had chosen to expand its coverage. Some of these people may migrate to receive coverage, thereby increasing costs for states that have expanded the program. This is known as the “welfare magnet” hypothesis, a claim that geographic variation in social programs induces the migration of welfare recipients to places with more generous benefits or eligibility. To investigate whether such spillover effects are likely, we used data from the Current Population Survey to examine the migration patterns of low-income people before and after recent expansions of public insurance in Arizona, Maine, Massachusetts, and New York. Using difference-in-differences analysis of migration in expansion and control states, we found no evidence of significant migration effects. Our preferred estimate was precise enough to rule out net migration effects of larger than 1,600 people per year in an expansion state. These results suggest that migration will not be a common way for people to obtain Medicaid coverage under the current expansion and that interstate migration is not likely to be a significant source of costs for states choosing to expand their programs.