Human leukocyte antigen system A (HLA) genes, especially HLA-C^* 06:02, have been proposed as major candidate genes for psoriasis, which is a T-cell driven immune disease that shows altered keratinocyte differentiation. Herein I would like to summarize an immunogenetic approach to psoriasis, which is a description of research that was mainly carried out by my colleagues during my service as Professor and Chairman (1997-2016) at the Department of Dermatology, Yamaguchi University Graduate School of Medicine.