Gilbert disease is a benign disorder of the bilirubin conjugation, which affects 7-10% of the average population. The symptoms are usually only mild jaundice and the slightly elevated unconjugated bilirubin level, other laboratory tests and the liver functions are usually normal. In most cases, mutation of the UDP glucuronyltransferase gene leads to impaired bilirubin conjugation. Besides the usual laboratory methods, genetic analyses of the UDP glucuronyltransferase gene can help in the diagnosis. In 80-100% of the patients the (TA)-insertion in the promoter-region of the gene is present in homozygous - (TA) 7 /(TA) 7 - form, and leads to the decrease of the amount of functionally active enzyme. The role of missense mutations localized in the coding region has not been clarified yet, but their co-occurrence with the (TA) 7 promoter-variant might mean an explanation to the elevated bilirubin level, jaundice, and the familiar aggregation of Gilbert disease.