BACKGROUND: Patients are increasingly paying for more of their medical care through cost-sharing, yet little is known about how patients change the ways that they seek care in response. OBJECTIVE: We sought to assess how patients change their care-seeking behavior in response to emergency department (ED) copayments. RESEARCH DESIGN: Telephone interviews with a stratified random sample of adult members of a large integrated delivery system. SUBJECTS: There were 932 respondents (72% response rate). MEASURES: We examined participants’ knowledge of their copayment level for ED services, and measures of how the cost-sharing affected their decisions about where or when to seek care. RESULTS: Overall, 82% of participants faced a copayment for ED services (ranging between 5 US dollars and 100 US dollars), and 41% correctly reported the amount of this copayment. In response to the perceived copayment amount, 19% reported changing their care-seeking behavior within the previous 12 months: 12% sought care from an alternate delivery site, 12% contacted a provider by telephone or the Internet, 9% delayed going to the ED, and 2% avoided medical care altogether. In multivariate models, the ED cost-sharing amount was significantly associated with reporting changes in care-seeking behavior. CONCLUSIONS: When faced with an ED copayment, patients in the health system most commonly shifted toward seeking care from other available alternatives, and rarely avoid medical care altogether.