A Search for WIMP Nuclear Recoils Underground: First Five-Tower Data from CDMS Abstract: Dark matter is concentrated in the halos of galaxies, including the Milky Way. If WIMPs make up these halos they should be detected via scattering from atomic nuclei in a terrestrial detector of nuclear recoils. In order to achieve sensitivity to WIMP nuclear recoils the experiment needs excellent background rejection and to be inside neutron and gamma-ray shields such as hydrogenated material, lead and the earth crust (underground). Nuclear recoils from cosmogenic fast neutrons in underground laboratories are one of the most challenging backgrounds to WIMP detection and are estimated using Monte-Carlo simulations. The first WIMP-search results from the Cryogenic Dark Matter Search (CDMS-II) experiment running with its full complement of 30 cryogenic particle detectors half a mile underground will be presented. Furthermore, neutron background studies will be discussed including the design of an instrument capable of benchmarking the Monte-Carlo simulations by measuring, for the first time, the rate of high-energy neutrons at the Soudan Underground Laboratory.