Abstract. Based directly on the DOSXYZ code created for the EGS4 code system, DOSXYZnrc is a Monte Carlo simulation code for determining dose distributions in a rectilinear voxel phantom. The OMEGA-BEAM system of codes created at NRC includes DOSXYZnrc. Every voxel may have a different density and substance. A variety of beams, including complete phase-space files from BEAMnrc and beams described using Beam Characterization models, may be incident on the phantom. A CT data set of Hounsfield numbers may be read in and converted by the companion application ctcreate into the details required by DOSXYZnrc to simulate transport in a phantom (i.e. the appropriate material and density are specified in each voxel)[1]. This CT phantom can be incident on any of the available beams. The code has a restart feature and may be executed on platforms for parallel computing.