Four males, the sons of 2 sisters, apparently have a new syndrome of mental retardation, seizures and psoriasis. Due to the relationship between the affected males we propose the inheritance to be X-linked recessive although cosegregation of two separate disorders may be occurring. Psoriasis has never been reported as a monogenic disorder. Results of cytogenetic studies, including fra (X) and high-resolution prometaphase analysis, were negative. Steroid sulfatase activities of cultured fibroblasts from 2 surviving affected males were normal. The results of HLA typing of all available relatives did not indicate a strong association between the skin disorder and certain HLA antigens. A healthy sister, who may be heterozygous carrier of the mutant X chromosome, decided on termination of 3 successive pregnancies after prenatal male sex determinations. Her fourth pregnancy with a female fetus is ongoing.