OBJECTIVES: This study explores the duration that patients stay in the emergency department (ED) for visits where they are treated and released. Duration for treat-and-release (T&R) ED visits is assessed by admission day and hour, patient demographics and hospital characteristics. METHODS: A retrospective data analyses was conducted to characterize the duration of T&R ED visits.  Duration for each visit was computed by taking the difference between admission and discharge times. Sensitivity analyses were performed to assess the robustness of results. The Healthcare Cost and Utilization Project (HCUP) State Emergency Department Databases (SEDD) for 2008 were used in the analysis.  The SEDD employed in this study include 4.7 million T&R ED visits in Arizona, Massachusetts, and Utah.  RESULTS: Duration varied significantly across admission hour and day of the week.  At 95th percentile, the average duration of T&R ED visits were longer (197.8 – 202.6, minutes). The average duration for patients admitted at 8 a.m. on Mondays, other weekdays, and weekend were respectively 184, 189, and 172 minutes.  Similarly, the average duration for patients admitted at 4 p.m. (12a.m.) on Mondays, other weekdays, and weekend were respectively 210, 202 and 179 (231, 246 and 234)  minutes. Medicare patients have the longest average duration (238 minutes). Black patients have 22 minutes longer duration compared to white patients.  There was significant variation in average duration across disease groups (e.g., 284 minutes for mental disorders and 160 minutes for injury and poisoning related diseases). The average duration at teaching (non-teaching) hospitals was 225 (166) minutes.  Hospitals with large bed size were associated with the longest duration of visits (222 minutes) when compared to hospitals with small bed size (172 minutes). CONCLUSIONS: The duration of T&R ED visits varied significantly across patient characteristics, hospital characteristics, admission hour, and day of the week.