Background: An Apparent Life-Threatening Event (ALTE) is an important challenge for the pediatrician, which requires guidelines for finding the etiology and making appropriate clinical decisions. Objective: To describe etiologies and clinical features of ALTE in infants, as determined by a standarized protocol. Methods: A prospective study including infants admitted to the Emergency Room and hospitalized due to an ALTE between May 2002 and May 2005. They were evaluated with an established protocol that considers the episode description, clinical history, and complementary laboratory studies. Results: 109 patients with ALTE and a mean age of 11 weeks had the following symptoms: apnea (100%), skin color changes (97%), and muscle tone changes (83%). 96% received CPR maneuvers or strong stimulation maneuvers for ending the episode. Fourteen percent of the cases were idiopathic, while other etiologies included respiratory infections (46%), gastroesophageal reflux (16%), seizures (6%), and urinary tract infections (6%). 3 patients expired. Conclusions: With this protocol, based on tools available in most public tertiary hospitals in Chile, we can identify the causes of ALTE similar to those reported in other studies, howeber with a lesser percentage of idiopathic episodes