We describe a rare case of double-lined frontoparietal scleroderma en coup de sabre. The relationship to the distribution following the lines of Blaschko is discussed. In addition, we present a genetic hypothesis which is based on a mosaic state induced by postzygotic mosaicism. A patient with scleroderma en coup de sabre has a mosaic state for genes which predispose to susceptibility for linear scleroderma.