A methodology for simulating seismic damage of unreinforced mansonry buildings for seismic risk assessment of urban areas is presented in this paper. The methodology is based on the Italian vulnerability index and on the results of a post earthqueke damage survey study whose main result was an observed vulnerability function. The Monte Carlo method was than used to simulate damage probability matrices, fragility curves and vulnerability functions, all of which are the basis of a seismic risk study. The simulation process required the generation of thousands of hypothetical buildings, the analysis of their seismic behaviour and probabilistic studies of the computed results. As an example, probable damage scenarios werw developed for an urban area of Barcelona, Spain.