To identify HLA markers that may contribute to the genetic susceptibility of Koreans to psoriasis, we studied 84 psoriasis patients, with serologic HLA types of A, B, and genotypes of HLA-Cw, DRB1, DQA1, DQB1, DPB1 alleles. The distribution of HLA markers and the associated haplotypes were analyzed according to age and sex. HLA-Cw*0602 showed the strongest association with psoriasis (relative risk = 36.0, p < 10-8, Pc < 8 x 10-7). The frequencies of A1 (relative risk = 17.0, p < 9 x 10-7, Pc < 7 x 10-5), A30 (relative risk = 5.5, p < 2 x 10-5, Pc < 0.001), B13 (relative risk = 5.6, p < 4 x 10-6, Pc < 3 x 10-4), B37 (relative risk = 30.3, p < 7 x 10-7, Pc < 6 x 10-5), DRB1*07 (relative risk = 5.9, p < 2 x 10-6, Pc < 8 x 10-5), DRB1*10 (relative risk = 26.4, p < 4 x 10-6, Pc < 3 x 10-4), DQA1*02 (relative risk = 6.2, p < 5 x 10-7, Pc < 4 x 10-4), DQB1*02 (relative risk = 2.5, p < 0.005, Pc = ns) and DPB1*1701 (relative risk = 24.6, p < 9 x 10-6, Pc < 7 x 10-4) were also significantly increased in Korean psoriasis patients. Type I and type II psoriasis were subdivided into groups of below and above 30 y of age, because of the significant difference found in HLA-Cw*0602 phenotype frequency between the two groups (83.9% vs. 54.5%, p < 0. 009). In addition to HLA-Cw*0602, the frequencies of B37 and DPB1*1701 were significantly higher in type I as opposed to type II psoriasis. HLA-A30-B13-Cw*0602-DRB1*07-DQA1* 02-DQB1*02 was identified as a high risk haplotype. This was particularly true at an early age in the female. HLA-A33-B44-Cw*1401-DRB1*13-DQA1* 01-DQB1*06-DPB1*0401 was defined as a protective haplotype for psoriasis. The extended haplotype HLA-A1-B37-Cw*0602-DRB1*10-DQA1*01-DQB1*05 was discovered to be a high-risk factor in Koreans. To summarize, this study demonstrates the differential association of HLA according to sex, and identifies a newly found high-risk haplotype and a protective haplotype in Korean psoriasis patients.