The IXth International Congress of Paediatrics selected Kernicterus as one of the major topics for discussion in recognition of the significant advances made in medical knowledge of this problem during the past decades. The discussion, carried on by an international panel of leading clinicians and basic scientists, was lively and informative. Since the Congress the participants have prepared their papers for presentation in book form, providing illustrations and references, and taking account of the newest material pertaining to the subject. In this volume emphasis is laid on the examination of the various etiological factors which may lead to the development of hyperbilirubinemia, and of the factors which then may facilitate the development of secondary brain damage. There is a collaborative effort to present material which will help physicians in the prevention of this condition and in the improvement of their methods of treatment of it. The introductory panel examines the incidence and clinical course of Kernicterus in premature infants and especially the factors, other than immune haemolytic disease, which many lead to the development of it. Other papers provide statistical material on the incidence of Kernicterus of prematurity, re-evaluate concepts of physiological jaundice, report studies of the question of whether hyperbilirubinemia is premature could lead to neurological sequelae in later life, outline the factors which may influence the life span of the red blood cells in the newborn, describe the distribution and the metabolism of bilirubin in the body and the mechanism of its excretion, and give a pathology of Kernicterus in both humans and animals. It is established that the blood levels of bilirubin cannot be relied upon exclusively to indicate the degree of danger of development of Kernicterus.