Gilbert syndrome (GS) is a hereditary relatively common benign unconjugated hyperbilirubinaemia. The promoter region of uridine diphosphate glycosyltransferase 1 (UGT1A1) gene contains a normal A (TA)6TAA element; variations in this motif (A(TA)7/8TAA) are generally associated with this disorder. This is a report of the varied effects of GS in a Mexican Mestizo family with a non-common (TA)8 repeat in this population. The proposita and her mother showed (TA)7/(TA)8 genotype, while her father and sister were (TA)6/(TA)7, but only the proposita showed clinical manifestations. This report supports that the (TA)7 and (TA)8 are necessary, but not enough to explain the features of GS. There are probably additional genetic variations ie, the presence of “modifier” genes or one can speculate that an oligogenetic trait can contribute to the expression of the final phenotype.