This work proposes a methodology for the probabilistic simulation of the transverse failure of Carbon Fibre Reinforced Polymers (CFRP) by analyzing the random distribution of the fibres within the composite. First chapters are devoted to the State-of-the-art review on the modelization of random materials, the computation of effective properties and the transverse failure of fibre reinforced polymers. The first step in the proposed methodology is the definition of a Statistical Representative Volume Element (SRVE) which has to satisfy a set of statistical and mechanical criteria. Next, a methodology for the statistical analysis of the distribution of the fibre within the composite from digital images of the transverse section is described. This analysis is performed for four different materials. Finally, a two-scale computational method for the transverse failure of unidirectional laminae is proposed. This method is able to provide probability density functions of the mechanical variables in the composite. Some applications and possibilities of the method are given and the simulation results are compared with experimental tests.