OBJECTIVES: Emergency department (ED) utilization is often used as an indicator of poor chronic disease control and/or poor quality of care. We sought to determine if 2 ED utilization measures identify clinically or demographically different populations of children. STUDY DESIGN: Retrospective cohort study utilizing IBM Health/Truven MarketScan Medicaid data. METHODS: Children and adolescents were categorized based on the presence and complexity of chronic medical conditions using the 3M Clinical Risk Group system. Children and adolescents were categorized as high ED utilizers using 2 measures: (1) ED reliance (EDR) (number of ED visits / [number of ED visits + number of ambulatory visits]; EDR >0.33 = high utilizer) and (2) visit counts (≥3 ED visits = high utilizer). Logistic regression models identified patient factors associated with each of our outcome measures. RESULTS: A total of 5,438,541 children and adolescents were included; 65% were without chronic disease (WO-CD), 32% had noncomplex chronic disease (NC-CD), and 3% had complex chronic disease (C-CD). EDR identified 18% as frequent utilizers compared with 7% by the visit count measure. In the visit count model, children younger than 2 years and those classified as WO-CD and NC-CD were less likely to be identified as high utilizers. Conversely, in the EDR model, children and adolescents 2 years and older and those classified as WO-CD and NC-CD were more likely to be classified as high utilizers. CONCLUSIONS: The ED utilization measures identify clinically and demographically different groups of patients. Future studies should consider the medical complexity of the population being studied before choosing the most appropriate measure to employ.