Dowling-Degos disease (DDD) is an autosomal-dominant genodermatosis characterized by reticulate pigmentation of the flexures. By direct DNA sequencing, we have identified a frameshift mutation in exon 1 of KRT5 in the proband from an extended Spanish DDD kindred. Cloning of PCR products confirmed that this was a 2-bp deletion mutation, designated c.442delAG, leading to a premature termination codon in the V1 domain of the K5 polypeptide, designated p.S148fsX30. These data confirm that haploinsufficiency for K5 causes DDD and points to a prominent role for the keratin intermediate filament cytoskeleton within basal keratinocytes in epidermal pigment biology.