A case is presented in which X-linked ichthyosis was diagnosed prenatally using fluorescence in situ hybridization. Fetal sex was known by second trimester ultrasound in a woman with very low second trimester MSUE3. All of the 15 maternal peripheral blood metaphase spreads examined displayed two hybridization signals on one X chromosome (one in the steroid sulfatase region (Xp22.3) and one in the centromeric region), but only one hybridization signal (in the X centromeric region) on the other X chromosome. Thus, one of the X chromosome had a deletion in the Xp22.3 region, a result which was consistent with carrier status for steroid sulfatase deficiency and X-linked ichthyosis. In the 15 metaphase spreads that were examined from the amniotic fluid sample, the X chromosome displayed one hybridization signal in the control region, but no hybridization signal in the steroid sulfatase region. Thus, the X chromosome of this male fetus had a deletion in the steroid sulfatase region, a result that was consistent and demonstrated postpartum X-linked ichthyosis.