The dependence of the domain structure on poling for (001)-oriented Pb(Mg1/3Nb2/3)O-3-x%PbTiO3 crystals with x=20, 30, 35, and 40 has been investigated by scanning force microscopy in the piezoresponse mode and by polarized optical microscopy. The results demonstrate a domain hierarchy on various length scales, ranging from nanometers to millimeters, which is notably dependent upon the electrical history of the specimen. The results provide important insights into the nature of the domain engineered state in these crystals. (C) 2005 American Institute of Physics.