Study objective Although repeated intubation attempts are believed to contribute to patient morbidity, only limited data characterize the association between the number of emergency department (ED) laryngoscopic attempts and adverse events. We seek to determine whether multiple ED intubation attempts are associated with an increased risk of adverse events. Methods We conducted an analysis of a multicenter prospective registry of 11 Japanese EDs between April 2010 and September 2011. All patients undergoing emergency intubation with direct laryngoscopy as the initial device were included. The primary exposure was multiple intubation attempts, defined as intubation efforts requiring greater than or equal to 3 laryngoscopies. The primary outcome measure was the occurrence of intubation-related adverse events in the ED, including cardiac arrest, dysrhythmia, hypotension, hypoxemia, unrecognized esophageal intubation, regurgitation, airway trauma, dental or lip trauma, and mainstem bronchus intubation. Results Of 2,616 patients, 280 (11%) required greater than or equal to 3 intubation attempts. Compared with patients requiring 2 or fewer intubation attempts, patients undergoing multiple attempts exhibited a higher adverse event rate (35% versus 9%). After adjusting for age, sex, principal indication, method, medication, and operator characteristics, intubations requiring multiple attempts were associated with an increased odds of adverse events (odds ratio 4.5; 95% confidence interval 3.4 to 6.1). Conclusion In this large Japanese multicenter study of ED patients undergoing intubation, we found that multiple intubation attempts were independently associated with increased adverse events.