An apparent life-threatening event (ALTE) is defined as an episode that is frightening to the observer and involves a period of apnea, transient color change (usually pale or cyanotic), and a transient change in tone (limp or stiff). According to the conventional use of ALTE, these infants appear well on presentation to the emergency department. Once it is determined that an ALTE has occurred, the workup typically includes a thorough history and physical exam; vital signs including temperature, HR, RR, and pulse oximetry; and a bedside glucose. Additional laboratory investigations are rarely helpful in the ED and should be directed by the initial history and vital signs but may include: a complete blood count; electrolytes, calcium, phosphorous, magnesium, and ammonia levels; urine toxicological screen; chest radiograph; electrocardiogram; and a septic workup, including blood, urine, and cerebrospinal fluid. Unless the history clearly suggests a benign etiology such as reflux, infants with ALTE are typically admitted to the hospital for further workup and apnea monitoring. The utility of apnea monitoring (particularly in the home) has been recently questioned. At the conclusion of hospitalization, diagnoses of infants with ALTE often remain elusive. When identified, etiologies range from GERD to seizures, inborn errors of metabolism, lower respiratory tract infection, pertussis, gastroenteritis, asthma, head injury, feeding difficulties, and urinary tract infections. There is no relation between ALTEs and sudden infant death syndrome which are now considered distinct entities.