Lichen striatus (LS) is an asymptomatic, spontaneously resolving linear dermatosis consisting of 2 to 4 mm flat topped papules following the lines of Blaschko. Two siblings presented with a simultaneous occurrence of LS along the same Blaschko line of the left upper extremity. Only four other cases of a simultaneous occurrence of LS in related siblings have been reported, but none of these have occurred in the same extremity. Although 10 years have passed since the last case report of this unique concurrent familial eruption, few discoveries have been made regarding its etiology. Several theories have been proposed including environmental agents, cutaneous injury, viral infection, hypersensitivity, and genetic predisposition. These theories are discussed along with retrotransposons, a possible new explanation for the pathogenesis of this and other Blaschko line disorders.