A complete three-dimensional simulation tool for X-ray scatter imaging experiments was developed. This tool is able to compute the interaction of the incoming X-ray beam with a 3D sample having defined X-ray cross-sections and to record the radiation detected by the collimation-detection system. The physical model of the interaction includes X-ray absorption, and elastic as well as inelastic scattering. The philosophy was to develop an efficient code with a high degree of flexibility in the choice of the experiment geometry and of the properties of the individual components to aid design optimization and data correction procedures of X-ray scatter experiments. Tests on representative case studies will be described. As a useful byproduct, a correction matrix is easily obtained that can be used to minimize the well known problem of attenuation effects in the acquired X-ray scatter images.