BACKGROUND: Admitted and discharged patients with prolonged emergency department (ED) stays may contribute to crowding by utilizing beds and staff time that would otherwise be used for new patients. OBJECTIVES: To describe patients who stay > 6 h in the ED and determine their association with measures of crowding. METHODS: This was a retrospective, observational study carried out over 1 year at a single, urban, academic ED. RESULTS: Of the 96,562 patients seen, 16,017 (17%) stayed > 6 h (51% admitted). When there was at least one patient staying > 6 h, 60% of the time there was at least one additional patient in the waiting room who could not be placed in an ED bed because none was open. The walk-out rate was 0.34 patients/hour when there were no patients staying in the ED > 6 h, vs. 0.77 patients/hour walking out when there were patients staying > 6 h in the ED (p < 0.001). When the ED contained more than 3 patients staying > 6 h, a trend was noted between increasing numbers of patients staying in the ED > 6 h and the percentage of time the ED was on ambulance diversion (p = 0.011). CONCLUSION: In our ED, having both admitted and discharged patients staying > 6 h is associated with crowding. Copyright 2010 Elsevier Inc. All rights reserved.