Abstract: The Polycystic Ovary Syndrome (PCOS) is one of the most common endocrine disorders in females of reproductive age. The etiology of PCOS has been involved in a combination of genetic and environmental factors. Recently, several studies with different ethnical groups have been demonstrated that the Single Nucleotide Polymorphism (SNP) of insulin receptor (INSR) gene is associated with susceptibility to the PCOS. This study was undertaken to analyze the influence of the SNP of INSR on PCOS in a Korean population. We studied 50 PCOS and 35 normal patients. According to the Body Mass Index (BMI), subjects were classified into two groups (lean and obese based on the number same or higher than 25 kg m 2) and analyzed the association of SNP in the INSR gene with PCOS. As shown with controls, PCOS patients were more frequent for the T allele (the CT and TT genotypes) at the exon 17 of the INSR. Interestingly, the frequency of the C allele in patients with PCOS was significantly higher than that in normal controls (40% vs. 8.57%, p = 0.001). Various frequencies for the SNP of INSR among different ethnical backgrounds suggest that the ethnical background should be considered to determine the relationship between the SNP of INSR and PCOS.