A perfect separation of the solid phase from its equilibrium liquid phase is usually assumed in the papers on crystallization system synthesis. In practice, a considerable amount of solution may accompany the crystalline phase separated. In multi-unit crystallization systems with recycle streams, the imperfect phase separation affects the flow rates of all process streams and may even lead to the process infeasibility. The influence of separation efficiency in the process units on the performance of a three-stage crystallization process with one solid and one liquid recycle has been examined.