AbstractBackground  To evaluate the distributions of the human leukocyte antigen (HLA) at class I and II loci that may contribute to the genetic susceptibility to psoriasis patients in the north‐eastern Thai population.Materials and methods  We analyzed the allelic frequencies of HLA class I and II by using the polymerase chain reaction‐amplification refractory mutation system (PCR‐ARMS) technique and polymerase chain reaction‐single stranded conformation polymorphism (PCR‐SSCP), respectively, in 140 north‐eastern Thais with psoriasis that were sudivided into two groups: one with age at onset < 40 years (type I psoriasis; 95 cases) and the other with age at onset > 40 years (type II psoriasis; 45 cases). Three hundred healthy unrelated north‐eastern Thais were used as controls.Results  HLA‐A*01, ‐A*0207, ‐A*30, ‐B*08, ‐B*13, ‐B*4601, ‐B*57, ‐Cw*01, ‐Cw*0602, and ‐DRB1*07 were positively associated with type I psoriasis, whereas HLA‐A*24, ‐A*33, and ‐Cw*04 were negatively associated with type I psoriasis with statistical significance when compared to the controls. The Cw*0602 allele showed the strongest correlation with this type. In addition, the frequencies of HLA‐A*0207, ‐A*30, ‐Cw*01, and ‐DRB1*1401 were significantly increased in type II psoriasis. HLA‐A*207, ‐B*4601, ‐Cw*01, ‐DRB1*09, ‐DQB1*0303 (AH46.1), HLA‐A*01‐B*57‐Cw*0602‐DRB1*07‐DQB1*0303 (AH57.1), and HLA‐A*30, ‐B*13, ‐Cw*0602, ‐DRB1*07, and ‐DQB1*02 (AH13.1) were identified as high‐risk major histocompatibility complex (MHC) halotypes for psoriasis patients in the early onset group in north‐eastern Thais.Conclusions  This study demonstrates not only the differential association between HLA markers and types of psoriasis according to age at onset, but also a newly found high‐risk and a protective haplotype in Thai psoriasis patients.