Hydrocyclones belong to an important group of equipments designed to solid-liquid or liquid-liquid separation in a centrifugal field. It is possible to adapt a hydrocyclone to the accomplishment of several industrial activities depending on the geometrical relations among its main dimensions. The operation and design of these devices are relatively simple; however, the flow inside them is very complex and its prediction is very difficult. For that reason, most models that are used to predict hydrocyclone performance are empirical ones. The objective of this work was to study the influence of geometric variables in the performance of hydrocyclones, using CFD and response surface techniques. The obtained results show that it was possible to find an optimum hydrocyclone design, that is, geometric relationships that lead to Euler number and cut size in minimum levels.