The most important steps of bilirubin metabolism involved in the pathophysiology of neonatal hyperbilirubinemia are: 1) hemoglobin degradation by heme oxygenase; 2) bilirubin binding to serum albumin; 3) bilirubin conjugation to acid glucoronic by glucoronyl transferase. Progress in the knowledge of these metabolic steps allows to understanding of why massive hemolysis, infections, hypoxia and prematurity increase the risk of kernicterus and therefore justify adapted preventive and therapeutic measures.