This analysis examines how often patients get hit with surprise medical bills, what circumstances tend to give rise to them and what proposals are being considered to protect consumers from this problem. The study of claims data from large employer health plans finds that in roughly 1 of every 6 emergency room visits and inpatient hospital stays in 2017, patients came home with at least one out-of-network medical bill. More specifically, 18 percent of all emergency visits and 16 percent of in-network hospital stays had at least one out-of-network charge, leaving patients at risk for surprise medical bills. The risk of getting a surprise bill is much greater in some states. For instance, emergency care visits were more likely to result in at least one out-of-network charge in Texas, New Mexico, New York, California and Kansas, and less likely in Minnesota, South Dakota, Nebraska, Alabama and Mississippi. The analysis is part of the Peterson-Kaiser Health System Tracker, an online information hub dedicated to monitoring and assessing the performance of the U.S. health system.