We present an easily fabricated waveguide prism for the terahertz (THz) frequency range. The prism is made of polypropylene and uses waveguide dispersion to spatially separate frequencies over the range of 0.1 to 0.7 THz. The diffraction properties of the prism were determined using electromagnetic field simulations and the waveguide parameters were optimized to maximize frequency dispersion. Angular-dependent measurements of two prisms designs were obtained in a terahertz timedomain goniometer setup. An excellent match between simulation and measurement was found. The prism can be used as a dispersive element in novel THz systems for a variety of applications. © 2013 Optical Society of America.