Gilbert and Crigler-Naijar syndromes are familial unconjugated hyperbilirubinemias caused by genetic lesions involving a single complex locus encoding for bilirubin UDP-glucuronosyltransferase (UGT1A1) gene. Over the last years, a number of different mutations affecting this gene have been characterized. In this report is provided a summary of reported Gilbert and Crigler-Najjar syndromes-associated UGT1A1 gene mutations. (c) 2005 Elsevier Inc. All rights reserved.