We experienced a case of a 19-year-old man with Gilbert syndrome with concomitant hereditary spherocytosis. The patient presented with moderate unconjugated hyperbilirubinemia, and inherited etiology was strongly suspected. The diagnosis of Gilbert syndrome was confirmed by the genetic analysis of the UGT1A1 gene, demonstrating UGT1A1*28 and compound heterozygote UGT1A1*6. In addition, since the laboratory findings and imaging studies revealed lysemia as well as gallstone and splenomegaly, a diagnosis of hereditary spherocytosis was made as a comorbidity. Both Gilbert syndrome and hereditary spherocytosis are hereditary diseases with a high frequency, and the hyperbilirubinemia may be exacerbated when these two diseases are concomitant.