['Hospitals around the United States are advertising emergency department (ED) wait times. The objective was to measure the difference between publicly posted and actual ED wait times and to compare these between ED site volumes.', 'This study was a retrospective consecutive sample of ED patients at one hospital system with four EDs. The wait times of 8,889 patients were included in this analysis. One ED was in a large teaching hospital with 5,000 ED patients per month; the other three were freestanding or community EDs without teaching and with fewer than 2,000 ED patients per month each. The publicly posted ED wait times at the time of patient arrival were recorded and compared to the actual wait times as retrieved from the ED tracking system. The difference between posted and actual wait times for each site was calculated. Separate one-way analysis of variance (ANOVA) tests with post hoc testing were conducted to assess actual wait time and wait time difference between ED sites.', 'Mean and standard deviation (SD) wait time difference at the main ED with a volume of 5,000 patients per month was 31.5 (±61.2) minutes. At the facilities with fewer than 2,000 ED patients per month each, the differences in wait times were 4.2 (±21.8), 8.6 (±23.8), and 1.3 (±11.9) minutes. ANOVA results revealed that the main ED had significantly different actual wait time and wait time differences (p < 0.05) when compared to the other three EDs.'] Are posted emergency department wait times always accurate?