Objectives: Emergency departments (EDs) are recognized as a high-risk setting for prescription errors. Pharmacist involvement may be important in reviewing prescriptions to identify and correct errors. The objectives of this study were to describe the frequency and type of prescription errors detected by pharmacists in EDs, determine the proportion of errors that could be corrected, and identify factors associated with prescription errors. Methods: This prospective observational study was conducted in a tertiary care teaching ED on 25 consecutive weekdays. Pharmacists reviewed all documented prescriptions and flagged and corrected errors for patients in the ED. We collected information on patient demographics, details on prescription errors, and the pharmacists' recommendations. Results: A total of 3,136 ED prescriptions were reviewed. The proportion of prescriptions in which a pharmacist identified an error was 3.2% (99 of 3,136; 95% confidence interval [CI] 2.5-3.8). The types of identified errors were wrong dose (28 of 99, 28.3%), incomplete prescription (27 of 99, 27.3%), wrong frequency (15 of 99, 15.2%), wrong drug (11 of 99, 11.1%), wrong route (1 of 99, 1.0%), and other (17 of 99, 17.2%). The pharmacy service intervened and corrected 78 (78 of 99, 78.8%) errors. Factors associated with prescription errors were patient age over 65 (odds ratio [OR] 2.34; 95% CI 1.32-4.13), prescriptions with more than one medication (OR 5.03;, and those written by emergency medicine residents compared to attending emergency physicians (OR 2.21, 95% CI 1.18-4.14). Conclusions: Pharmacists in a tertiary ED are able to correct the majority of prescriptions in which they find errors. Errors are more likely to be identified in prescriptions written for older patients, those containing multiple medication orders, and those prescribed by emergency residents. RÉ SUMÉObjectifs: C'est connu, les services d'urgence (SU) sont un lieu où le risque d'erreurs de prescription est é levé . Alors, les pharmaciens peuvent jouer un rô le important dans la ré vision des prescriptions dans le but de repé rer et de corriger les erreurs. L'é tude avait pour objectifs de dé crire la fré quence des erreurs de prescription dé celé es par les pharmaciens au SU et leur type, de dé terminer la proportion des erreurs susceptibles de correction et de cerner les facteurs associé s aux erreurs de prescription. Medication errors are one of the most common types of ED errors. 3,5,6 Most medication errors are related to one or more of ''five wrongs'' involved in the act of prescribing: wrong drug, wrong dose, wrong route, wrong time, and wrong patient. 7,8 Certain types of drugs, such as analgesics, antibiotics, sedatives, and cardiovascular drugs, have been associated with more frequent prescription errors compared to other drug classes. 3,7,9 In addition, prescribing to more complex and acutely ill patients at nighttime, on weekends, or by trainees has been associated with more frequent errors. 7,9 Previous studies have estimated the proportion of ...