The objective of this study was to determine the rate of positive ED diagnostic evaluations and significant interventions during the hospitalization of infants after an apparent life-threatening event (ALTE). The study was performed at a single, tertiary care children's hospital. Patients under 6 months of age were identified for a potential ALTE from the ED chief complaint log. The charts of patients meeting the definition of an ALTE were abstracted for data pertaining to the patient's history, physical examination, ED diagnostic evaluation, and admission. The yield of the ED diagnostic evaluation and hospitalization was noted. A positive ED evaluation was defined as a diagnostic intervention that resulted in a specific treatment for a defined condition. Significant medical interventions were derived from a validated instrument assessing the risk of admission for pediatric patients presenting to an ED. Such interventions included, but were not limited to, parenteral antibiotics for documented infections, supplemental oxygen, endotracheal intubation, airway suctioning, and intensive-care unit admission. Over a 5-year period with 253,408 patient visits, 523 patents met the initial search criteria for a potential ALTE. From this group, 483 charts were reviewed (92.4%) and 150 patients met the definition for an ALTE. The mean age of the patients was 61.7 days and 115 (76.7%) were admitted. Of the patients with an ALTE, 122 patients had ED diagnostic tests performed and three had a positive result (2.5%; 95% confidence interval [CI]; 0.5-7.0). The rate of significant medical interventions among admitted patients was 7.% (9 of 115, 95% CI, 3.6-14.3). No patients with a positive ED diagnostic evaluation were discharged from the ED. Risk factors for significant medical interventions included prematurity, a positive medical history, and age >60 days. The overall rate of either positive ED diagnostic evaluations or significant medical interventions during hospitalizations of infants after an ALTE is low. A majority of these patients can be best managed with a limited ED diagnostic evaluation and a period of observation.