Lamellar ichthyosis (LI) is an autosomal recessive disorder of cornification. Mutations in the transglutaminase 1 gene (TGM1) have been identified in several families with this disorder. We analyzed two unrelated families with offspring affected with LI. Family 1 included affected monozygotic twins, in which a homozygous G-to-T transversion was identified in exon 6 at amino acid residue R315L. This mutation was also identified in the unaffected mother. In family 2, which consisted of one affected infant, a T-to-G transversion in exon 8 resulted in a change of phenylalanine to valine, F400V, and a C-to-T transition in exon 4 resulted in a change of proline to leucine, P248L. In this family, the mutation F400V was found in the unaffected father, and the mutation P248L was identified in the unaffected mother. These findings extend the growing body of literature documenting mutations in the TGM1 gene as the molecular basis of certain cases of lamellar ichthyosis.