['Despite the growing problems of emergency department (ED) crowding, the potential impact on the frequency of medication errors occurring in the ED is uncertain. Using a metric to measure ED crowding in real time (the Emergency Department Work Index, or EDWIN, score), we sought to prospectively measure the correlation between the degree of crowding and the frequency of medication errors occurring in our ED as detected by our ED pharmacists.', "We performed a prospective, observational study in a large, community hospital ED of all patients whose medication orders were evaluated by our ED pharmacists for a 3-month period. Our ED pharmacists review the orders of all patients in the ED critical care section and the Chest Pain unit, and all admitted patients boarding in the ED. We measured the Spearman correlation between average daily EDWIN score and number of medication errors detected and determined the score's predictive performance with receiver operating characteristic (ROC) curves.", "A total of 283 medication errors were identified by the ED pharmacists over the study period. Errors included giving medications at incorrect doses, frequencies, durations, or routes and giving contraindicated medications. Error frequency showed a positive correlation with daily average EDWIN score (Spearman's rho = 0.33; P = .001). The area under the ROC curve was 0.67 (95% confidence interval, 0.56-0.78) with failure defined as greater than 1 medication error per day."] Is eD overcrowding associated with an increased frequency of medication errors?