The incidence and temporal patterns of gastroesophageal reflux (GER) in infants presenting with an apparent life-threatening event (ALTE) was compared with GER characteristics of infants evaluated for persistent emesis, utilizing continuous 24 h intraesophageal pH monitoring. These data indicate that the incidence of significant GER was similar in both groups, despite the absence of a clinical vomiting history in 46% of ALTE patients. Furthermore, infants with ALTE demonstrate a significantly higher incidence of sleep reflux when compared with control infants presenting with vomiting alone (27 vs. 0%, p less than 0.001). Awake GER beyond the first two postprandial hours was not observed in either study group. Monitoring results, therefore, indicate that significant GER is common in infants with ALTE; and these infants manifest an apparently unique pattern of GER distinct from that observed in age-matched controls with GER alone. Possible relationships between GER in ALTE patients and the development/onset of apneic episodes are discussed.