ObjectiveTo describe the demographics and clinical outcomes of infants with brief resolved unexplained events (BRUE).DesignA retrospective cohort study.Setting11 centres within the Canadian Paediatric Inpatient Research Network.PatientsPatients presenting to the emergency department (ED) following a BRUE (2017–2021) were eligible, when no clinical cause identified after a thorough history and physical examination.Main outcome measuresSerious underlying diagnosis (requiring prompt identification) and event recurrence (within 90 days).ResultsOf 1042 eligible patients, 665 were hospitalised (63.8%), with a median stay of 1.73 days. Diagnostic tests were performed on 855 patients (82.1%), and 440 (42.2%) received specialist consultations. In total, 977 patients (93.8%) were categorised as higher risk BRUE per the American Academy of Pediatrics guidelines. Most patients (n=551, 52.9%) lacked an explanatory diagnosis; however, serious underlying diagnoses were identified in 7.6% (n=79). Epilepsy/infantile spasms were the most common serious underlying diagnoses (2.0%, n=21). Gastro-oesophageal reflux was the most common non-serious underlying diagnosis identified in 268 otherwise healthy and thriving infants (25.7%). No instances of invasive bacterial infections, arrhythmias or metabolic disorders were found. Recurrent events were observed in 113 patients (10.8%) during the index visit, and 65 patients had a return to ED visit related to a recurrent event (6.2%). One death occurred within 90 days.ConclusionsThere is a low risk for a serious underlying diagnosis, where the majority of patients remain without a clear explanation. This study provides evidence-based risk for adverse outcomes, critical information to be used when engaging in shared decision-making with caregivers.