STUDY OBJECTIVE: To elucidate risk factors for apnea in preterm infants discharged from the hospital and in full-term healthy infants. To determine the efficacy of real-time cardiopulmonary monitoring versus computerized storage and retrieval for infants at risk. STUDY DESIGN: Prospective study. SETTING: Operating rooms and pediatric patient care units of university medical center. PATIENTS: 27 preterm infants and 20 full-term infants no more than 60 weeks' post-conceptional age, who were admitted for elective herniorrhaphy. INTERVENTIONS: Infants were monitored before and after herniorrhaphy with general anesthesia using an infant apnea impedance monitor, pulse oximetry, and nursing observation. MEASUREMENTS AND MAIN RESULTS: Demographic information and medical history were correlated with postoperative apnea. The sensitivity and specificity of nursing observation and oximetry were compared with computerized apnea monitors. Five patients (11%, four preterm, one full-term) were apneic postoperatively as recorded by computerized pneumocardiography. Previous apnea history, gestational age at birth, and postconceptional age at operation positively correlated with postoperative apnea. Nursing observation failed to detect 4 of 5 patients with documented apnea (sensitivity 20%, positive predictive value 50%). Pulse oximetry failed to detect 3 of 5 patients with apnea (sensitivity 40%, positive predictive value 66%). CONCLUSIONS: Although it is easier to predict postoperative respiratory dysfunction in previously sick or very young infants, absolute predictability for all neonates remains elusive. Clinical monitors with both storage and retrieval capabilities and real-time monitoring increase our ability to detect significant events in children at risk for apnea after herniorrhaphy.