This paper presents an example of 3DEC modelling of a rock tunnel using geological mapping obtained from 3D images of terrestrial laser scanner and the discrete fracture network approach. Three main discontinuity sets were identified in an 8-m-long section of a tunnel constructed in gneiss. The amount of discontinuity data obtained by 3D Terrestrial laser scanner mapping allowed the application of several sophisticated discontinuity analysis (orientation, size and frequency), and probability density functions were defined. These functions were used as input to discrete fracture network modeling, leading to a more representative 3DEC block model. Thus, if the mechanical characterization of the rock mass is also properly made, this approach can be used for stability analysis in rock mechanics. Specifically, it could be very useful for analyzing sections of uncoated tunnels in which the rock mass is strongly fractured.