As part of a patient-based case-control study of newborn encephalopathy, we examine the cranial ultrasound results of 212 patients to determine the validity of ultrasound in predicting an adverse outcome. Forty-six (22%) patients died or developed cerebral palsy (adverse outcome) by 2 years of age. On the basis of clinical decision, 125 (60%) patients had an ultrasound before 72 hours of age; of these, 29% had an adverse outcome. The resistive index is the primary measure of interest, with a value of 0.55 or less considered abnormal. Infants with an abnormal resistive index are 8.8 times (P <0.001) more likely to have an adverse outcome than those with a normal result. The positive predictive value of an abnormal resistive index was 71%. The results are similar for the subgroup with intrapartum hypoxia and the subgroup that had ultrasound performed before 24 hours of age. It is clear that resistive index results cannot be used in isolation, although they may have a place, in combination with other factors, in the counseling of parents and, cautiously, in the clinical management of patients. (C) 2002 by Elsevier Science Inc. All rights reserved.