Psoriasis vulgaris is associated with the HLA‐Cw6 and Cw7 antigens. However, it has not yet been clarified if the HLA‐Cw6 and Cw7 genes themselves are the susceptible gene related to this disease or if it is some other non‐HLA gene in a linkage disequilibrium with these HLA‐C alleles. The S gene, recently identified in the HLA class I region 160 kb telomeric of HLA‐C, encodes a keratin‐like protein and is expressed specifically in the granular layer of the epidermis. Therefore, it is tempting to speculate that the S gene is one of the strong candidate genes responsible for the pathogenesis of psoriasis vulgaris. Direct sequencing of the first and second exon of the S gene after polymerase chain reaction (PCR) amplification has allowed the identification of two diallelic polymorphic sites in exon 1 and seven diallelic polymorphic sites in exon 2, three among which result in amino acid exchanges, a Ser‐Phe substitution at amino acid position 186, a Gly‐Val substitution at position 393 and a Ser‐Leu substitution at position 394. No significant difference in the dimorphic distributions of the S gene was observed between the patients with psoriasis vulgaris and healthy controls, suggesting that the susceptible gene for psoriasis is not the S gene itself.