Abstract: A psoriasis susceptibility locus defined as among linked members within a family has been identified. The locus is linked to an intron of the interleukin enhancer binding factor gene in some families, while being linked to an interleukin 8 gene in other families demonstrating a familial linked form of psoriasis. The locus identified may be further defined as being located distal to genetic maker D17S784 of human chromosome 17q. This locus does not demonstrate linkage with DNA markers within flanking the HLA cluster of genes. A psoriasis susceptibility locus has also been observed close to the centromere of human chromosome 4. Both identified regions provide positive LOD scores with markers on chromosomes 17q and particularly 2 regions close to the ILF gene or the interleukin 8 gene. Methods of screening a family for psoriasis susceptibility using a defined familial psoriasis susceptibility locus are also disclosed.