Routine ultrasound evaluation of neonates and young infants for congenital dislocation of the hip has been recommended. We have used the methods of decision analysis to determine whether every neonate should be examined by ultrasound or just those at increased risk. We have also studied the reliability and accuracy of ultrasound in following infants during observation and treatment, using published data. We find that ultrasound is not the preferred strategy for the screening of neonates, and that its role in evaluating high-risk patients depends on the point of view. For an individual, when third parties are bearing the cost, ultrasound is useful. For society as a whole, the routine ultrasound evaluation of the high-risk patient is not advantageous. For follow-up, ultrasound using the methods of Graf has a low reliability and there are no adequate data for methods using dynamic assessment.