Keratin 5 is the major type II keratin of the basal cells of epidermis and of other stratified epithelia. With its type I partner, keratin 14, it constitutes a major fraction of the cytoskeleton of the basal cells. Epidermolysis bullosa simplex with mottled pigmentation (EBS-MP) is a rare dermatologic disorder of autosomal dominant inheritance with intraepidermal blistering after minor trauma, reticular hyperpigmentation unrelated to the blistering, nail dystrophy, and mild palmoplantar keratosis. Keratin 5 and keratin 14 are known to be essential for the basal keratinocyte cytoskeleton and are defective in several forms of epidermolysis bullosa simplex. Recently, a 71C-->T transition in the keratin 5 gene (KRT5) causing a P24L substitution was identified in some patients with EBS-MP.