Rapid precipitation of both organic and inorganic compounds at high supersaturation requires homogenous mixing to control the particle size distribution. We present the design and characterization of a new multi-inlet vortex mixer (MIVM). The four-stream MIVM allows control of both the supersaturation and the final solvent quality by varying stream velocities. The design also enables the separation of reactive components prior to mixing. Finally, the design enables mixing of streams of unequal volumetric flows, which is not possible with alternate confined impinging jet mixing geometries. We characterize the mixing performance of the MIVM using competitive fast reactions (the so-called "Bourne reactions"). Adequate micromixing is obtained with a suitably defined Reynolds number when Re > 1600. The experimental results are compared to computational fluid dynamics (CFD) simulations of the fluid mechanics and parallel reactions in the MIVM. Excellent correspondence is found between the simulation and the experimental results with no adjustable parameters. The CFD simulations provide a powerful tool for the optimization of these complex mixing geometries. (C) 2007 Published by Elsevier Ltd.