Twenty-three cases of placental steroid sulfatase deficiency are reported. All children were boys who later acquired ichthyosis of the recessive X-linked type. The steroid sulfatase deficiency was present in placental tissue, umbilical cord leucocytes, and cultured skin fibroblasts of affected boys. An antepartum diagnosis can be obtained either by detecting the enzyme deficiency in cultured amniotic fluid cells or by finding an elevated total excretion of androstenetriol , 16 alpha-hydroxy-dehydroepiandrosterone, and 16 alpha-hydroxy-pregnenolone in maternal third-trimester urine. Vaginal delivery was accomplished in 16 patients (70%). No conspicuous pregnancy complications or neonatal problems were noted. However, birth weights tended to be relatively low. Intervention is unnecessary unless other obstetric indications require it. The incidence of this disorder appears to be approximately one per 2000 male births.