Objective To observe clinical features and identify causative genes of reticulate pigmented anomaly of the flexures in a pedigree.Methods A survey was conducted in a pedigree with reticulate pigmented anomaly of the flexures.Clinical manifestations were recorded in details for each patient in this pedigree.Tissue specimen was obtained from the proband for histopathological examination and ultrastructural observation.Mutation scanning was carried out by PCR and direct sequencing in 3 patients in the family.Results All the patients in this pedigree presented with reticular pigmentation of the flexures and idiopathic guttate hypomelanosis on the abdomen and back.Histopathological and ultrastructural study revealed epidermal hyperpigmentation with an increase in melanin content in epidermal keratinocytes but no changes in the number of melanocytes.No mutation was found in the KRT5 gene in this family.Conclusions This is the first case report of reticulate pigmented anomaly of the flexures associated with idiopathic guttate hypomelanosis.No mutation is identified in the KRT5 gene of patients with reticulate pigmented anomaly of the flexures in this family,indicating the existence of other causative genes.