Importance: To encourage the appropriate utilization of emergency care, cost-sharing for emergency care was increased from HK$100 (US $12.8) to HK$180 (US $23.1) per visit in June 2017 in all public hospitals in Hong Kong. However, there are concerns that this increase could deter appropriate emergency department (ED) visits and be associated with income-related disparities. Objective: To examine changes in ED visits after the fee increase. Design, Setting, and Participants: This retrospective cohort study used administrative data from June 2015 to May 2019 from all public hospitals in Hong Kong. Participants included all Hong Kong residents aged 64 years and younger, categorized into low-income, middle-income, and high-income groups according to the median household income in their district of residence. Data analysis was performed from May to June 2023. Main Outcomes and Measures: The primary outcome was the ED visit rate per 100 000 people per month, categorized into 3 severity levels (emergency, urgent, and nonurgent). Secondary outcomes include general outpatient (GOP) visit rate, emergency admission rate, and in-hospital mortality rate per month at public hospitals. Segmented regression analyses were used to estimate changes in the level and slope of outcome variables before and after the fee increase. Results: This study included a total of 5441679 ED patients (2606332 male patients [47.9%], 2108933 patients [38.5%] aged 45-64 years), with 2 930 662 patients (1407885 male patients [48.0%], 1111804 patients [37.9%] aged 45-64 years) from the period before the fee increase. The fee increase was associated with an 8.0% (95% CI, 7.1%-9.0%) immediate reduction in ED visits after June 2017, including a 5.9% (95% CI, 3.3%-8.5%) reduction in urgent visits and an 8.9% (95% CI, 8.0%-9.8%) reduction in nonurgent visits. In addition, a 5.7% (95% CI, 4.7%-6.8%) reduction of emergency admissions was found, whereas no significant changes were observed in in-hospital mortality. Specifically, a statistically significant increase in GOP visits (4.1%, 95% CI, 0.9%-7.2%) was found within the low-income group, but this association became insignificant after controlling for the social security group, who were exempted from payment, as a control. Conclusions and Relevance: In this cohort study, the fee increase was not associated with changes in ED visits for emergency conditions, but there was a negative and significant association with both urgent and nonurgent conditions across all income groups. Considering the marginal increase in public GOP services, further study is warranted to examine strategies to protect low-income people from avoiding necessary care.. © 2023 American Medical Association. All rights reserved.