Pedigree analysis of ichthyosiz vulgaris in an extensive North German kindrcd revealed X-linked recessive inheritance. Only males were affected; heterozygous females had no sign of this dermatosis. Clinically and histologically, the disease resembled the autosomal dominant form. The differential diagnosis between this X-linked recessive ichthyosis vulgaris, ichthyosiz congenita mitis, and X-linked ichthyosis of the Wells-Kerr type is discussed. We conclude from our qtudy that ichthyosis vulgariz is genetically heterogeneous.