BACKGROUND AND OBJECTIVES: Some children repeatedly use the emergency department (ED) at high levels. Among Medicaid-insured children with high-frequency ED use in 1 year, we sought to describe the characteristics of children who sustain high-frequency ED use over the following 2 years. METHODS: Retrospective longitudinal cohort study of 470 449 Medicaid-insured children appearing in the MarketScan Medicaid database, aged 1-16 years, with >/=1 ED discharges in 2012. Children with high ED use in 2012 (>/=4 ED discharges) were followed through 2014 to identify characteristics associated with sustained high ED use (>/=8 ED discharges in 2013-2014 combined). A generalized linear model was used to identify patient characteristics associated with sustained high ED use. RESULTS: A total of 39 945 children (8.5%) experienced high ED use in 2012, accounting for 25% of total ED visits in 2012. Sixteen percent of these children experienced sustained high ED use in the following 2 years. Adolescents (adjusted odds ratio [aOR]: 1.4 [95% confidence interval: 1.3-1.5]), disabled children (aOR: 1.3 [95% confidence interval: 1.1-1.5]), and children with 3 or more chronic conditions (aOR: 2.1, [95% confidence interval: 1.9-2.3]) experienced the highest likelihood for sustaining high ED use. CONCLUSIONS: One in 6 Medicaid-insured children with high ED use in a single year experienced sustained high levels of ED use over the next 2 years. Adolescents and individuals with multiple chronic conditions were most likely to have sustained high rates of ED use. Targeted interventions may be indicated to help reduce ED use among children at high risk.