Hereditary spherocytosis (HS) is an inherited disorder characterized by intrinsic defects in the red cell membrane proteins. The molecular abnormality is heterogeneous and may affect several membrane proteins including spectrin, ankyrin, band 3 and protein 4.2. Most patients have icterus and cholestasis due to chronic hemolysis. Gilbert’s syndrome (GS) is a metabolic disorder characterized by a mild and chronic unconjugated hyperbilirubinemia in the absence of liver and hematologic disease. A polymorphism in the promoter of UGT1A1 gene has been shown to associate GS with a decrease of enzymatic activity to about 30%. The co-inheritance of HS and GS can exacerbate hyperbilirubinemia, and, therefore, it could be a confounding factor to define HS severity. The aim of our study was to evaluate the prevalence of GS in HS patients. We evaluated the bilirubin plasmatic level and the TA duplication in the repetitive TATA box sequence of the UGT1A1 gene promoter in 27 HS patients and 60 healthy individuals.