Modelling of the injection moulding process is carried out in this work on the basis of Williams and Lord model and its recent extensions to postfilling stages. The emphasis is devoted to identifying the role of crystallisation kinetics in the process simulation. Data of pressure histories during injection moulding of an iPP are taken as reference to the analysis. Crystallisation kinetics of the material was described by means of a nonisothermal formulation of Avrami model whose parameters where determined either by accounting for only of calorimetric results or by describing also final density data of thin samples subjected to characterised quenching histories. Predictions of pressure histories are analysed in relation to the crystallisation kinetics adopted. The effect of pressure on crystallisation is also discussed.