Monilethrix is an autosomal dominant hair disorder characterized by a beaded appearance of the hair resulting from periodic thinning of the shaft (MIM 158000). The phenotype shows variable penetrance and results in hair fragility and patchy dystrophic alopecia. Mutations of the helix-encoded region in two hair-specific keratins (hHb1 and hHb6) have been identified as responsible for this disorder. We investigated two unrelated families from Russia and Colombia with monilethrix and found two missense mutations in hHb6. In the Russian family, we found a G to A transition at the first base of codon 402, resulting in a lysine substitution (GAG to AAG), designated E402K. In the Colombian family, affected patients carried a missense mutation of codon 413, involving a transition from G to A causing a lysine substitution (GAG to AAG), designated E413K. These two mutations have been identified in other monilethrix families from Europe. Our findings extend the body of evidence implicating recurrent hHb6 and hHb1 mutations in monilethrix families from around the world.