A group of hereditary palmoplantar keratodermas due to heterozygous mutation in the loricrin gene has recently been identified. Of five reported pedigrees, four presented as mutilating keratoderma with ichthyosis (variant Vohwinkel syndrome), and one as progressive symmetric erythrokeratoderma. We report a new Japanese pedigree of loricrin keratoderma. A 14-year-old male and his 11-year-old female sibling had both been born as collodion babies and were initially diagnosed as having non-bullous congenital ichthyosiform erythroderma, but later developed palmoplantar keratoderma with pseudoainhum. Their father was similarly affected. Direct sequencing of genomic DNA revealed a G residue insertion at codon 230-231 of the loricrin gene. Antibody studies confirmed the presence of mutant loricrin in the retained nuclei. We conclude that loricrin gene mutation may present as congenital ichthyosiform erythroderma, and should be included in the differential diagnosis of collodion baby.