In the pharmaceutical industry a growing number of applications employ polymeric nanoparticles. In order to produce suitable particulate systems it is important to accurately control both particle size and morphology. In this work turbulent precipitation by solvent displacement of poly-epsilon-caprolactone (PCL) in water-acetone mixtures by using Confined Impinging Jets Reactors (CIJRs) is investigated. Our experimental data show that the effects of mixing and of the geometrical characteristics of the CIJR on the particle size distribution are quite important, and the origin of these effects is interpreted by resorting to computational fluid dynamics simulations. Eventually the possibility of exploiting these effects through an Adjustable Confined Impinging jets Reactor (ACIJR) is demonstrated at a proof of concept level. (C) 2008 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.