We present radio images with the Australia Telescope of a sample of powerful radio galaxies. The observations were designed to be sensitive to the largest-scale structures in the radio sources. The morphologies are representative of radio galaxies with FRII type structures and with sizes exceeding 1Mpc. We observe the giant source to have the same axial ratios as those in smaller sources with similar radio powers. Moreover, the deviations from axial symmetry are also observed to be linearly scaled from sources an order of magnitude smaller. The observations are indicative of self-similar evolution in the morphologies of powerful radio galaxies.