The comparative frequency with which the human leukocyte antigen (HLA)-A, -B, -C and -DR were to be found in 54 insulin-dependent diabetes mellitus (IDDM) patients and 73 individuals unafflicted with diabetes in Korea was determined. There was no association between HLA-B8, -B15, or -Bw54 and IDDM. However, an increased frequency of HLA-B13 was found in a segment of the entire population and the entire population of patients: that group of patients in which the onset occurred before the age of 15 years(juvenile-onset IDDM) (p<.01) and that entire population of patients in which the onset found to be before the age of 30 years (entire IDDM) (p<.01). HLA-B35 was found to be significantly decreased in frequency only in the entire IDDM(p<.05). A significant increase in the frequency of HLA-DR4 was found in the entire IDDM patients; HLA-DR4 was found in 55.6% of the patients versus 31.5% of the controls. However, the negative correlation between HLA-DR2 and IDDM was statistically significant in those with juvenile-onset IDDM. It is concluded that the HLA pattern and its association witH IDDM in Korea would appear to be different from that in most other racial groups, including Caucasians, Japanese, and Chinese.