Many astrophysical models predict a diffuse flux of ultra high-energy neutrinos from active galactic nuclei and other extragalactic sources. AMANDA-II (Antarctic Muon and Neutrino Detector Array) is a large volume neutrino telescope, designed to measure the energetic neutrino flux from these astrophysical sources. A search for diffuse neutrinos with energies in excess of 105 GeV has been conducted with AMANDA-II data recorded between 2000 and 2002. The primary background for this analysis is bundles of downgoing, high-energy muons from the interaction of cosmic rays in the atmosphere. A method for separating these ultra high-energy neutrinos from the background is discussed, and the results of this search are presented.