A recent genome-wide association analysis of psoriasis identified IL12B and IL23R as significantly associated with psoriasis. Here we report association test results of a Thai cohort consisting of 206 psoriasis cases and 114 controls. The IL23R SNPs rs7530511 and rs11209026, and IL12B SNPs rs3212227 and rs6887695 were genotyped using Taqman assays. Data were analyzed using a logistic regression model for linear trend of association. One of the IL23R markers, rs7530511, was marginally significant (P = 0.017). The other IL23R marker, rs11209026, was not polymorphic. One of the IL12B markers, rs3212227, showed significant association with psoriasis (OR = 1.64, P = 0.0058) while the other, rs6887695, did not (OR = 1.29, P = 0.12). Haplotype analysis of the two IL12B SNPs yielded highly significant association (P = 0.00081, OR = 1.73). These results showed that IL12B is an important genetic factor in psoriasis pathogenesis in the Thai population, with an association strong enough to yield significant confirmatory evidence using a modest sample size. Together with previously reported evidence for IL12B association in Caucasian, Japanese, and Chinese psoriatics, our results support the hypothesis that genes encoding components of the IL23-mediated inflammatory pathway are important determinants of psoriasis pathogenesis across multiple racial groups.