Frequent emergency department (ED) use is a public health and policy relevant concern but has not previously been examined in the Medicare population. We conducted a retrospective, claims-based analysis of a nationally representative 20% sample of fee-for-service Medicare beneficiaries in 2010 (n = 5,778,038) to examine frequent ED use. We used multinomial logistic regression to study the relationship between frequent ED use and sociodemographic, outpatient care, and clinical characteristics. Factors that were most strongly associated with frequent ED use included being age 18 to 34 years compared with 65 to 74 years (relative risk ratio = 20.5, confidence interval [CI; 19.7, 21.3]) and mental illness (relative risk ratio = 6.8, CI [6.7, 6.9]). Low versus high continuity of care was associated with 24% (95% CI [1.21, 1.26]) greater risk of frequent compared with non-ED use. Although clinical and demographic characteristics are most strongly associated with frequent ED use, poor continuity of care is also a contributor.