A 14-year-old boy is described with hypogonadism, ichthyosis and mental retardation. His karyotype was 46,Y, der(X),t(X;)(p22;q11). His mother's karyotype was 46,X,der(X),t(X;Y)(p22;q11). Thus the son is nullisomic for the region Xp22 leads to pter and the mother is monosomic for the same region. The steroid sulfatase activity in this boy is discussed in relationship to the enzyme's locus on the X chromosome and the manifestation of ichthyosis.