The classification of dispersed particles below 1 mu m is a difficult task due to the high surface area-to-volume ratio. Tubular-bowl centrifuges offer high centrifugal numbers, which enable the separation and classification of fine particles, biological cells and cell debris. This work presents the classification of two fine products with a mean particle size below 1 mu m. Polydisperse silica and polystyrene were split successfully into a fine and a coarse fraction by a semi-continuous tubular-bowl centrifuge. The fine fractions exhibited narrow particle size distributions. An optimization of the process could be achieved by a comprehensive understanding of the flow patterns, which are accessible with computational fluid dynamics. The axial and tangential velocity profiles were calculated for rotational speeds up to 40 000 rpm and throughputs ranging from 0.1 to 2 L/min.