Background: Return visits to the emergency department (ED) or hospital after an index ED visit strain the health system, but information about rates and determinants of revisits is limited. Objective: To describe revisit rates, variation in revisit rates by diagnosis and state, and associated costs. Design: Observational study using the Healthcare Cost and Utilization Project databases. Setting: 6 U.S. states. Patients: Adults with ED visits between 2006 and 2010. Measurements: Revisit rates and costs. Results: Within 3 days of an index ED visit, 8.2% of patients had a revisit; 32% of those revisits occurred at a different institution. Revisit rates varied by diagnosis, with skin infections having the highest rate (23.1% [95% CI, 22.3% to 23.9%]). Revisit rates also varied by state. For skin infections, Florida had higher riskadjusted revisit rates (24.8% [CI, 23.5% to 26.2%]) than Nebraska (10.6% [CI, 9.2% to 12.1%]). In Florida, the only state with complete cost data, total revisit costs for the 19.8% of patients with a revisit within 30 days were 118% of total index ED visit costs for all patients (including those with and without a revisit).