A methodology to evaluate the vulnerability and seismic risk of existing building structures in an urban area developed within a probabilistic scheme. It uses numerical procedures for the analysis of the non-linear seismic behaviour of structures and optimized sampling method and probabilistic models for the description of the obtained results. Occurrence probabilities for different damage levels of the structures in risk, corresponding to a giiven exposure period are thus obtained. From ail economical point of view, annual losses and minimum earthquake insurance taxes are evaluated. The proposed method is applied td the assessment of the seismic risk of a complete urban are a, located in the central part bf Barcelona, Spain, in which mostly unreiilforced masonry buildings and non-ductile reinforced concrete buildings are the most common building types. The method has been implemented, in a modular format in a Geographical Inforinatioil System, with the objetive of obtaining seismic risk scenarios.