Xu T, et al. - Patients who, often unknowingly, receive care from an out-of-network physician receive surprise medical bills from hospitals. These bills are typically many times the cost of care from an in-network physician and can be financially devastating. As per prior research, hospitals and departments within hospitals vary widely in hospital charge master prices, specifically the “markups” greater than Medicare reimbursement rates in medical bills for out-of-network care. To protect patients from surprise billing, including limiting the degree of markup, the US Congress is considering several approaches as of September 2019. In this cross-sectional study, markups from 2012 through 2016 were characterized and associations of markup with hospital characteristics were examined by focusing on charges in 2 specialties common in surprise medical billing, emergency medicine and anesthesiology, using internal medicine as a reference.