Only a few optical techniques are available to measure simultaneously the velocity and size of coarse particles dispersed in a fluid. Since particles are randomly shaped with a rough surface and inhomogeneous with respect to the refractive index, phase-based sizing techniques are not reliable. The applied optical sizing technique is based on light intensity measurement of a scattering particle crossing a top-hat laser beam. This optical set-up was first described by Grehan et al. In the range of geometrical optics, the sampled light at the receiving system is proportional to the square of the equivalent particle diameter within the diameter range 20-700 mu m. Velocity information is obtained by using a smaller concentric laser Doppler probe volume. Coincidence of the signals is guaranteed by the optical set-up, since the smaller probe volume diameter defines the triggering event. To demonstrate the performance of the system, some diameter distributions measured with the top-hat beam system are compared with results for a commercial laser diffraction system for different materials. The system is applied to obtain size-correlated velocity information of a particle-laden two-phase flow at a single-sided backward-facing step.