Effectiveness of hydrocyclone separations is highly dependent on their geometrical characteristics such as: chamber dimensions, aperture diameters or feed inlet geometry, for instance. Moreover, slight modifications of any of these features might severely affect separation efficiency. This work highlights the fundamental significance of the position of the vortex finder, showing how small changes in its length have meaningful effects on mass recovery and particle size distribution in overflow and underflow streams. This parameter has been scarcely considered in design studies. In order to establish the importance of the vortex finder length different and complementary methodologies were used such as mass balance, granulometric analysis and efficiency evaluation. Results obtained using theses methodologies were in agreement, showing that the highest efficient length of the vortex finder is 10% of the total length of the cyclone (0.1 L-t). This result was found for two hydrocyclones of different sizes, giving a more consistent conclusion. (C) 2007 Elsevier B.V. All rights reserved.