The aim of this experimental study is to investigate the separation performances of a new set of small cyclones. The diameter of these cyclones spans the range of 20-45 mm, which is the typical size of these devices when they are used for separating oil mist from blow-by gases in internal combustion engines. To reproduce the flow rates and oil load of combustion engines, we developed a flow bench, with a polydisperse aerosol generator producing engine oil droplets with diameter in a 0.3-10 mu m range. Measurements of the aerosol particle concentrations upstream and downstream of the cyclone permitted the determination of the particle collection efficiency, for the six devices that were tested, with flow rates ranging from 20 to 200 N1/min which are typical operating conditions. For the six cyclones, the geometry is normalized and all internal dimensions within the cyclone are proportional to its diameter. With the operating conditions of this study, the annular Reynolds number varied in the range 1.27 x 10(3) to 12.2 x 10(3). From the measured fractional collection efficiency curves, dimensionless cut-off aerodynamic diameters were determined. These measurements have been compared with available correlations for the determination of this dimensionless diameter as a function of the annular Reynolds number. Different correlations are proposed in this study, for the evaluation of the cut-off diameter and for the shape of the collection efficiency. We were able to establish that the collection efficiency curve dimensionless slope is correlated to a Reynolds number.