Mild isolated unconjugated hyperbilirubinaemia is incidentally or purposefully attained finding in 4-8% of population. Adolescence is a typical age for detection of hypebilirubinaemia. In these patients a mutation in gene-promoter for uridin-diphospho-glucuronyl-transpherase A 1, which determines development of the benign Gilbert's syndrome, is present in most of the cases. Although homozygote formation of this mutation was described in 11-16% of general population, only in a part of them hyperbilirubinaemia is manifested. Beginning or continuation of hyperbilirubinaemia in adolescent age is linked probably with some other changes in the hepatocyte and factors which influence it. Among adolescents with hyperbilirubinaemia, risk factors that can induce a metabolic liver overload have to be considered. They include oligosymptomatic or asymptomatic EBV infection, drug and alcohol abuse, hormonal contraception etc. These conditions must be respected in the regimen of these adolescents.