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Background: Although the HLA class II genes are cleaily associated with insulin-dependent diabetes mellitus(IDDM) in all ethnic. Groups, considerable variation in the associated genotypes is observed among the different ethnic groups. Mathods: In order to estimate what degree genetic and environmental determinants influence the true incidence of IDDM, ICA by imrnunohistochemistry, anti-GAD prevalence by radioimmunoprecipitation and HLA-DRB1, DQAl, and DQB1 polymorphisms after PCR amplification of genomic DNA were analyzed in 131 cases of IDDM, whose age at diagnosis were less than 15. Results: 56% of them(73/131) were anti-GAD positive. 43% IDDM(56/131) were ICA positive. HLA DR3 and DR9 were susceptibility markers, whereas DR2 and DR5 were protective markers. DR3/4,, DR3/9, and DR3/X(X: other than 3, 4) were susceptible genotypes. HLA DQA1*0301 allele was increased, and DQB1*0301 and DQB1*0602 were decreased in IDDM. Not only HLA DQA1 Arg, but also DQBl non-Asp were found to be independent marker for IDDM, but their strength of association was weak. The highest prevalence of anti-GAD was observed in thosc homozygous for DR4(87.5%), exceeding that(47.8%) in those without this allele, and those with one DR4(63.5), whereas the highest prevealence of ICA was found in those homozygous for DR3(10G%), exceeding that in those with one DR3(64.3%) or in those without this allele(36.7%). There was a significant difference in numbers of HLA DQ susceptibility heterodimers in anti-GAD positive or negative patients. Conelusion: The prevalence of islet-specific auto- antibodies were present at comparable sensitivity and specificity in Korean IDDM patients. We could also assess that the immunoenetic markers for IDDM among Caucasians likewise confer disease susceptibi- lity among Koreans. However, different HLA suscep- tibility alleles and a lower strength of association with known susceptibility markers, presumably because of differences in the genetic make-up of the population or in linkage disequilibrium patterns compared with other racial groups.