In this work the effect of molecular parameters (molecular weight (M-W), molecular weight distribution (MWD)) and processing conditions (crystallization temperature, flow conditions) on the isothermal crystallization behavior of three isotactic poly-l-butene (iPB) samples is investigated by means of rheo-optical techniques. The emphasis in this paper will be on the kinetics and the resulting morphology. Turbidity measurements show a strong effect of M-W and the degree of undercooling on the flow-induced crystallization (FIC), whereas the effect of MWD is not quite clear. Scaling relations, proposed in literature, that are based on polymer chain relaxation were found to predict correctly the dependence of FIC, at least when samples of similar MWD are considered. A mastercurve is presented combining effects of M-W, shear strain, shear rate and temperature. Optical microscopy observations provide information on the quiescent growth rate and the morphology of the crystallites. The effect of the different parameters on the observed transition from an isotropic morphology at low shear rates to a rod-like crystalline structure at high shear rates, could again be explained in terms of polymer chain relaxation. (c) 2006 Elsevier Ltd. All rights reserved.