The effect of the nitrogen purge, monomer purification, type of agitation, and presence of costabilizer on the particle size distribution (PSD) was investigated in the dispersion polymerization of styrene in ethanol and in the dispersion copolymerization of styrene and butyl acrylate in a water-ethanol mixture. Purging with nitrogen and, to a lesser extent, monomer purification, were of paramount importance to achieve monodispersity. The type of agitation had a weak effect on the PSD, whereas the presence of costabilizer had no effect on the PSD.