Antisolvent crystallization systems and methods are provided that employ porous hollow fiber membranes. The porous hollow fiber membrane includes a plurality of porous hollow fibers positioned within a shell, each porous hollow fiber defining a lumen side and shell side. A crystallizing solution is introduced to one side of the hollow fibers and an antisolvent is introduced to the other side of the fibers, in either cocurrent or countercurrent flow. One of the antisolvent and the crystallizing solution permeates in part through the porous hollow fiber membrane to the other side and crystals are formed thereby. Permeation of the antisolvent or the crystallizing solution establishes advantageous radial mixing that facilitates crystal formation of a desired size distribution. Downstream mixing, e.g., a completely stirred tank or a static mixer, may be employed to further improve crystallization operations.