Controlled release poly(lactic-co-glycolic acid) microparticles for use as active pharmaceutical ingredient carriers were prepared by the emulsion extraction method. Particle formation experiments were carried out in a stirred vessel. The local flow conditions in these experiments, that is, local shear rates and dissipation rates, and the extraction rate of the organic solvent were examined by a computational fluid dynamics (CFD) simulation. The local flow conditions in the stirred tank reactor have a significant influence on the final properties, specific surface area, skeletal density, organic solvent content, and size of the microparticles. We determined nondimensional correlations for predicting these particle properties as functions of the process parameters as, for example, the stirrer speed, emulsion injection point, and oil droplet size in the initial emulsion. The results demonstrate that CFD simulations offer insight into the particle formation process for different batch sizes and provide a basis for scale-up and optimization of the process. (c) 2012 American Institute of Chemical Engineers AIChE J, 59: 18681881, 2013