A probabilistic approach to estimate the expected seismic physical damage of existing buildings in urban areas is presented. The main steps of the procedure are seismic hazard, vulnerability and structural response. These three steps are undertaken with a fully probabilistic point of view. Seismic hazard is assessed by means of the annual rate of exceedance of a parameter quantifying the expected seismic action. Buildings may be characterized by a class in a building typology matrix and/or by a vulnerability index or, even, by its capacity curve, but in any case its seismic strength must be also defined in a probabilistic way. In the case of vulnerability index we can use beta or similar probability distributions. Finally, adequate empirical, semi-empirical or analytical damage functions or fragility curves may be used to estimate the expected damage. The method is enlightened by means of four cases, corresponding to two un-reinforced masonry buildings located in the Colima and Coatzacoalcos cities in México. The seismic risk computed for these cases is presented in terms of the annualized damage.