Psoriasis (OMIM*177900) is a common, chronic, hyperproliferative inflammatory disorder of the skin affecting approximately 2% of Caucasians. Despite the prevalence of psoriasis in general population, significant differences in the incidence among Japanese, Eskimos, West Africans, north American blacks and American natives are well known. The cause for these variations are likely to be both genetic and environmental. Independent genomewide scans have suggested the involvement of a large number of chromosomal regions (loci), but so far only poor susceptibility genes have been suggested. We discuss genetic basis of the disease, results and interpretations of relevant studies, with particular regard to study design and future perspectives. Indeed to date, mapping genes which contribute to complex diseases is one of the major challenge in the post-genomic era.