Using a simple and reliable isotropic wet etching process, we fabricated a microflow cytometer in which cells/particles are concentrated in the center of the sample stream using a 2-D hydrodynamic focusing technique and a microweir structure. Having focused the cells/particles, they are detected and counted using an LIF method. The experimental and numerical results confirm the effectiveness of the hydrodynamic sheath flows in squeezing the cells/particles into a narrow stream in the horizontal X-Y plane. Furthermore, it is shown numerically that the microweir structure results in the separation of the cells/particles in the vertical X-Z plane such that they pass through the detection region in a sequential fashion and can therefore be counted with a high degree of precision. The experimental results obtained using fluorescent polystyrene beads with diameters of 5 and 10 mu m, respectively, confirm the suitability of the proposed device for microfluidic applications requiring the high-precision counting of particles or cells within a sample flow.