PURPOSE: The incidence of neonatal hyperbilirubinemia is twice as high in East Asians as in Caucasians. However, its metabolic basis has not been clearly explained. The UDP-glucuronosyltransferase gene(UGT1A1) mutation was found to be a risk factor of neonatal hyperbilirubinemia. We studied whether neonatal hyperbilirubinemia is associated with the 1828G>A(rs 10929303) polymorphism of the UGT1A1 gene, which encodes for a key enzyme of bilirubin metabolism. METHODS: The genomic DNA was isolated from 80 Korean full term neonates who had greater than a 12 mg/dL level of serum bilirubin with no obvious cause, and the genomic DNA was also isolated from 164 Korean neonates of the control population. We studied a single nucleotide polymorphism (SNP) of 1828G>A in the untranslated region of the UGT1A1 gene by direct sequencing. RESULTS: Three of the 80 neonates with a serum bilirubin level above 12 mg/dL had homozygous mutations and 10 of the 80 neonates with a serum bilirubin level above 12 mg/dL had heterozygous mutations. Thirteen of the 164 neonates of the control group had homozygous mutations and 16 neonates of the control group had heterozygous mutations. The allele frequency of 1828G>A polymorphism of UGT1A1 in the hyperbilirubinemia group was 10.0 percent, which was not significantly different from the allele frequency of 12.8 percent in the control group. CONCLUSION: In this study, the 1828G>A polymorphism of the UGT1A1 gene was detected in the Korean neonates with neonatal hyperbilirubinemia. Our results indicated that this SNP is not associated with the prevalence of hyperbilirubinemia in Koreans.