This large multicenter trial tested whether cerebral cooling initiated within 6 hours of birth and continued for 72 hours would reduce the risk of death and moderate to severe neurodevelopmental injury at 18-22 months corrected age. Infants at least 36 weeks gestation with an abnormal blood gas within 1 hour of birth, or a history of an acute perinatal event and a 10-min Apgar score <5, or continued need for ventilation were screened. Following a neurological exam, those with moderate to severe encephalopathy were randomized to a 72-hour period of total body cooling (cooling blanket, followed by slow re-warming). The study was conducted in two phases: Phase I (20 infants) were examined for the safety of an esophageal temperature of 34-35 C; Phase II (main trial, 200 infants) were evaluated for the safety and efficacy of an esophageal temperature of 33-34 C. Cardio-respiratory, electroencephalograms (EEGs), renal, metabolic, and hematologic status, and esophageal and abdominal skin temperature were monitored during the 72 hours of intervention. Surviving children were given neurodevelopmental examinations at 18-22 months corrected age and again at school age (6-7 years of age).