Reticulate acropigmentation of Kitamura (RAK) is a rare genetic disorder of cutaneous pigmentation with an autosomal dominant pattern of inheritance and a high penetration rate. The characteristic skin lesions are reticulate, slightly depressed pigmented macules mainly affecting the dorsa of the hands and feet, which first appear before puberty and subsequently expand to the proximal limb and the trunk. To identify mutations that cause RAK, we performed exome sequencing of four family members in a pedigree with RAK. Fifty-three SNV/Indels were considered as candidate mutations after some condition narrowing. We confirmed the mutation status in each candidate gene of four other members in the same pedigree to find the gene that matched the mutation status and phenotype of each member. A mutation in ADAM10 encoding a zinc metalloprotease, a disintegrin and metalloprotease domain-containing protein 10 (ADAM10), was identified in the RAK family. ADAM10 is known to be involved in the ectodomain shedding of various substrates in the skin. Sanger sequencing of four additional unrelated RAK patients revealed four additional ADAM10 mutations. We identified a total of three truncating mutations, a splice site mutation and a missense mutation in ADAM10. We searched for mutations in the KRT5 gene, a causative gene for the similar pigmentation disorder Dowling-Degos disease (DDD), in all the patients and found no KRT5 mutation. These results reveal that mutations in ADAM10 are a cause of RAK and that RAK is an independent clinical entity distinct from DDD.