Abstract: A-genealogical investigation into 336 cases of psoriasis vulgaris among out-patients was made,and compared with the izicidence of psoriasis vulgaris of ordinary population in order to investigate into genetic rules of psoriasis.In 336 psoriatics,80 cases(23.80%) showed positive family history of psoriasis.At the same time the family members of 456 out-patients of various common skin diseases were investigated,and only 3 cases(0.65%) showed positive family history of psoriasis.