This report provides a brief preliminary account of the solution crystallization of isotactic polystyrene under the influence of velocity gradients. During crystallizations from 1,3,5-trimethylbenzene and cyclohexanol solutions, the polymer appears in a number of morphological forms which are composed of microfibrillar units. In isotactic polystyrene produced by heterogeneous Ziegler–Natta catalysis, similar microfibrillar units are observed. It is suggested, therefore, that these two apparently different processes have a common underlying mechanism in the formation of the microfibrils. The possible mechanisms of fibril formation are discussed.