A computer simulation of the Campanian Ignimbrite (Southern Italy) utilizes both forward and inverse techniques. The forward technique uses a given set of parameters (eruptive vent, initial velocity and rheology of the pyroclastic mass) to compute the trajectories and limits of pyroclastic flow propagation. The inverse approach, based on the Bayes theorem, calculates the probability density of the input parameters based on the limits of actual deposits in the field. The inverse method allows definition of the most likely set of eruption parameters consistent with the emplacement of the Campania Ignimbrite. These simulations furnish the following results: a) the Campanian Ignimbrite formation is compatible with a purely gravitative mode of movement; b) the areal distribution is consistent with a radial flow pattern from a limited vent area north of Naples; c) the most probable initial flow velocity is about 160 m/s which corresponds to a possible eruptive column height near 1.3 km. ¿ American Geophysical Union 1996